diff --git a/lib/reducers/user-reducer.js b/lib/reducers/user-reducer.js
--- a/lib/reducers/user-reducer.js
+++ b/lib/reducers/user-reducer.js
@@ -32,6 +32,7 @@
 } from '../ops/user-store-ops.js';
 import { stateSyncSpecs } from '../shared/state-sync/state-sync-specs.js';
 import { updateSpecs } from '../shared/updates/update-specs.js';
+import { processDMOpsActionType } from '../types/dm-ops.js';
 import type { BaseAction } from '../types/redux-types.js';
 import type { ClientUserInconsistencyReportCreationRequest } from '../types/report-types.js';
 import {
@@ -557,6 +558,28 @@
     }
 
     return [{ userInfos: action.payload.users }, [], []];
+  } else if (action.type === processDMOpsActionType) {
+    const newUserInfos = _keyBy(userInfo => userInfo.id)(
+      action.payload.userInfos,
+    );
+    const ops = convertUserInfosToReplaceUserOps(newUserInfos);
+    const processedUserInfos: UserInfos = processUserStoreOps(
+      state.userInfos,
+      ops,
+    );
+
+    if (_isEqual(state.userInfos)(processedUserInfos)) {
+      return [state, [], []];
+    }
+
+    return [
+      {
+        ...state,
+        userInfos: processedUserInfos,
+      },
+      [],
+      ops,
+    ];
   }
 
   return [state, [], []];
diff --git a/lib/shared/dm-ops/add-members-spec.js b/lib/shared/dm-ops/add-members-spec.js
--- a/lib/shared/dm-ops/add-members-spec.js
+++ b/lib/shared/dm-ops/add-members-spec.js
@@ -72,6 +72,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
       const currentThreadInfo: ThickRawThreadInfo = currentThreadInfoOptional;
@@ -110,6 +111,7 @@
     return {
       rawMessageInfos: [addMembersMessage],
       updateInfos,
+      userInfos: {},
     };
   },
 });
diff --git a/lib/shared/dm-ops/change-relationship-spec.js b/lib/shared/dm-ops/change-relationship-spec.js
new file mode 100644
--- /dev/null
+++ b/lib/shared/dm-ops/change-relationship-spec.js
@@ -0,0 +1,26 @@
+// @flow
+
+import type { DMOperationSpec } from './dm-op-spec.js';
+import type {
+  DMChangeRelationshipOperation,
+} from '../../types/dm-ops.js';
+import type { ClientUpdateInfo } from '../../types/update-types.js';
+
+const changeRelationshipSpec: DMOperationSpec<DMChangeRelationshipOperation> =
+  Object.freeze({
+    processDMOperation: async (
+      dmOperation: DMChangeRelationshipOperation,
+      viewerID: string,
+    ) => {
+      const { editorID, userID, relationship } = dmOperation;
+
+      const updateInfos: Array<ClientUpdateInfo> = [];
+      return {
+        rawMessageInfos: [],
+        updateInfos,
+        userInfos: {},
+      };
+    },
+  });
+
+export { changeRelationshipSpec };
diff --git a/lib/shared/dm-ops/change-thread-settings-spec.js b/lib/shared/dm-ops/change-thread-settings-spec.js
--- a/lib/shared/dm-ops/change-thread-settings-spec.js
+++ b/lib/shared/dm-ops/change-thread-settings-spec.js
@@ -57,6 +57,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
 
@@ -96,6 +97,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
 
@@ -107,6 +109,7 @@
           return {
             rawMessageInfos: [],
             updateInfos: [],
+            userInfos: {},
           };
         }
         changedFields.name = name;
@@ -138,6 +141,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
 
@@ -155,6 +159,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
 
@@ -183,6 +188,7 @@
       return {
         rawMessageInfos: generatedRawMessageInfos,
         updateInfos,
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/create-sidebar-spec.js b/lib/shared/dm-ops/create-sidebar-spec.js
--- a/lib/shared/dm-ops/create-sidebar-spec.js
+++ b/lib/shared/dm-ops/create-sidebar-spec.js
@@ -101,6 +101,7 @@
       return {
         rawMessageInfos: [], // included in updateInfos below
         updateInfos: [threadJoinUpdateInfo],
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/create-thread-spec.js b/lib/shared/dm-ops/create-thread-spec.js
--- a/lib/shared/dm-ops/create-thread-spec.js
+++ b/lib/shared/dm-ops/create-thread-spec.js
@@ -170,6 +170,7 @@
       return {
         rawMessageInfos: [], // included in updateInfos below
         updateInfos: [threadJoinUpdateInfo],
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/dm-op-specs.js b/lib/shared/dm-ops/dm-op-specs.js
--- a/lib/shared/dm-ops/dm-op-specs.js
+++ b/lib/shared/dm-ops/dm-op-specs.js
@@ -1,6 +1,7 @@
 // @flow
 
 import { addMembersSpec } from './add-members-spec.js';
+import { changeRelationshipSpec } from './change-relationship-spec.js';
 import { changeThreadSettingsSpec } from './change-thread-settings-spec.js';
 import { createSidebarSpec } from './create-sidebar-spec.js';
 import { createThreadSpec } from './create-thread-spec.js';
@@ -26,4 +27,5 @@
   [dmOperationTypes.LEAVE_THREAD]: leaveThreadSpec,
   [dmOperationTypes.REMOVE_MEMBERS]: removeMembersSpec,
   [dmOperationTypes.CHANGE_THREAD_SETTINGS]: changeThreadSettingsSpec,
+  [dmOperationTypes.CHANGE_RELATIONSHIP]: changeRelationshipSpec,
 });
diff --git a/lib/shared/dm-ops/join-thread-spec.js b/lib/shared/dm-ops/join-thread-spec.js
--- a/lib/shared/dm-ops/join-thread-spec.js
+++ b/lib/shared/dm-ops/join-thread-spec.js
@@ -40,6 +40,7 @@
       return {
         rawMessageInfos: [],
         updateInfos: [],
+        userInfos: {},
       };
     }
 
@@ -68,6 +69,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
       const currentThreadInfo: ThickRawThreadInfo = currentThreadInfoOptional;
@@ -105,6 +107,7 @@
     return {
       rawMessageInfos: [joinThreadMessage],
       updateInfos,
+      userInfos: {},
     };
   },
 });
diff --git a/lib/shared/dm-ops/leave-thread-spec.js b/lib/shared/dm-ops/leave-thread-spec.js
--- a/lib/shared/dm-ops/leave-thread-spec.js
+++ b/lib/shared/dm-ops/leave-thread-spec.js
@@ -27,6 +27,7 @@
       return {
         rawMessageInfos: [],
         updateInfos: [],
+        userInfos: {},
       };
     }
     const threadInfo: ThickRawThreadInfo = threadInfoOptional;
@@ -34,6 +35,7 @@
       return {
         rawMessageInfos: [],
         updateInfos: [],
+        userInfos: {},
       };
     }
 
@@ -69,6 +71,7 @@
     return {
       rawMessageInfos: [leaveThreadMessage],
       updateInfos,
+      userInfos: {},
     };
   },
 });
diff --git a/lib/shared/dm-ops/process-dm-ops.js b/lib/shared/dm-ops/process-dm-ops.js
--- a/lib/shared/dm-ops/process-dm-ops.js
+++ b/lib/shared/dm-ops/process-dm-ops.js
@@ -37,7 +37,7 @@
         console.log('ignored DMOperation because logged out');
         return;
       }
-      const { rawMessageInfos, updateInfos } = await dmOpSpecs[
+      const { rawMessageInfos, updateInfos, userInfos } = await dmOpSpecs[
         dmOp.type
       ].processDMOperation(dmOp, viewerID, utilities);
       dispatch({
@@ -45,6 +45,7 @@
         payload: {
           rawMessageInfos,
           updateInfos,
+          userInfos,
         },
       });
     },
diff --git a/lib/shared/dm-ops/remove-members-spec.js b/lib/shared/dm-ops/remove-members-spec.js
--- a/lib/shared/dm-ops/remove-members-spec.js
+++ b/lib/shared/dm-ops/remove-members-spec.js
@@ -28,6 +28,7 @@
         return {
           rawMessageInfos: [],
           updateInfos: [],
+          userInfos: {},
         };
       }
       const threadInfo: ThickRawThreadInfo = threadInfoOptional;
@@ -68,6 +69,7 @@
       return {
         rawMessageInfos: [removeMembersMessage],
         updateInfos,
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/send-edit-message-spec.js b/lib/shared/dm-ops/send-edit-message-spec.js
--- a/lib/shared/dm-ops/send-edit-message-spec.js
+++ b/lib/shared/dm-ops/send-edit-message-spec.js
@@ -39,6 +39,7 @@
       return {
         rawMessageInfos: [editMessage],
         updateInfos,
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/send-reaction-message-spec.js b/lib/shared/dm-ops/send-reaction-message-spec.js
--- a/lib/shared/dm-ops/send-reaction-message-spec.js
+++ b/lib/shared/dm-ops/send-reaction-message-spec.js
@@ -47,6 +47,7 @@
       return {
         rawMessageInfos: [reactionMessage],
         updateInfos,
+        userInfos: {},
       };
     },
   });
diff --git a/lib/shared/dm-ops/send-text-message-spec.js b/lib/shared/dm-ops/send-text-message-spec.js
--- a/lib/shared/dm-ops/send-text-message-spec.js
+++ b/lib/shared/dm-ops/send-text-message-spec.js
@@ -36,6 +36,7 @@
       return {
         rawMessageInfos: [textMessage],
         updateInfos,
+        userInfos: {},
       };
     },
   });
diff --git a/lib/types/dm-ops.js b/lib/types/dm-ops.js
--- a/lib/types/dm-ops.js
+++ b/lib/types/dm-ops.js
@@ -12,6 +12,10 @@
   rawMessageInfoValidator,
 } from './message-types.js';
 import type { ThickRawThreadInfo } from './minimally-encoded-thread-permissions-types.js';
+import {
+  type TraditionalRelationshipAction,
+  traditionalRelationshipActionsList,
+} from './relationship-types.js';
 import {
   type NonSidebarThickThreadType,
   nonSidebarThickThreadTypes,
@@ -22,6 +26,7 @@
 import { threadInfoValidator } from '../permissions/minimally-encoded-thread-permissions-validators.js';
 import { values } from '../utils/objects.js';
 import { tShape, tString, tUserID } from '../utils/validation-utils.js';
+import type { UserInfos } from './user-types.js';
 
 export const dmOperationTypes = Object.freeze({
   CREATE_THREAD: 'create_thread',
@@ -34,6 +39,7 @@
   LEAVE_THREAD: 'leave_thread',
   REMOVE_MEMBERS: 'remove_members',
   CHANGE_THREAD_SETTINGS: 'change_thread_settings',
+  CHANGE_RELATIONSHIP: 'change_relationship',
 });
 export type DMOperationType = $Values<typeof dmOperationTypes>;
 
@@ -249,6 +255,20 @@
     rawEntryInfos: t.list(rawEntryInfoValidator),
   });
 
+export type DMChangeRelationshipOperation = {
+  +type: 'change_relationship',
+  +editorID: string,
+  +userID: string,
+  +relationship: TraditionalRelationshipAction,
+};
+export const dmChangeRelationshipOperationValidator: TInterface<DMChangeRelationshipOperation> =
+  tShape<DMChangeRelationshipOperation>({
+    type: tString(dmOperationTypes.CHANGE_RELATIONSHIP),
+    editorID: tUserID,
+    userID: tUserID,
+    relationship: t.enums.of(traditionalRelationshipActionsList),
+  });
+
 export type DMOperation =
   | DMCreateThreadOperation
   | DMCreateSidebarOperation
@@ -259,7 +279,8 @@
   | DMJoinThreadOperation
   | DMLeaveThreadOperation
   | DMRemoveMembersOperation
-  | DMChangeThreadSettingsOperation;
+  | DMChangeThreadSettingsOperation
+  | DMChangeRelationshipOperation;
 export const dmOperationValidator: TUnion<DMOperation> = t.union([
   dmCreateThreadOperationValidator,
   dmCreateSidebarOperationValidator,
@@ -271,11 +292,13 @@
   dmLeaveThreadOperationValidator,
   dmRemoveMembersOperationValidator,
   dmChangeThreadSettingsOperationValidator,
+  dmChangeRelationshipOperationValidator,
 ]);
 
 export type DMOperationResult = {
   rawMessageInfos: Array<RawMessageInfo>,
   updateInfos: Array<ClientUpdateInfo>,
+  userInfos: UserInfos,
 };
 
 export const processDMOpsActionType = 'PROCESS_DM_OPS';
@@ -283,4 +306,5 @@
 export type ProcessDMOpsPayload = {
   +rawMessageInfos: $ReadOnlyArray<RawMessageInfo>,
   +updateInfos: $ReadOnlyArray<ClientUpdateInfo>,
+  +userInfos: UserInfos,
 };