diff --git a/lib/hooks/thread-hooks.js b/lib/hooks/thread-hooks.js
--- a/lib/hooks/thread-hooks.js
+++ b/lib/hooks/thread-hooks.js
@@ -5,7 +5,6 @@
 import uuid from 'uuid';
 
 import { useChatMentionContext } from './chat-mention-hooks.js';
-import { useGetCommFCUsersForFIDs } from './user-identities-hooks.js';
 import { removeUsersFromThreadActionTypes } from '../actions/thread-action-types.js';
 import genesis from '../facts/genesis.js';
 import { extractKeyserverIDFromID } from '../keyserver-conn/keyserver-call-utils.js';
@@ -18,8 +17,6 @@
 } from '../shared/dm-ops/dm-op-types.js';
 import { useProcessAndSendDMOperation } from '../shared/dm-ops/process-dm-ops.js';
 import {
-  useFetchFarcasterConversation,
-  useFetchFarcasterMessages,
   useUpdateFarcasterGroupNameAndDescription,
   useModifyFarcasterMembershipInput,
 } from '../shared/farcaster/farcaster-api.js';
@@ -58,7 +55,7 @@
 } from '../types/thread-types.js';
 import { values } from '../utils/objects.js';
 import { useDispatchActionPromise } from '../utils/redux-promise-utils.js';
-import { useSelector, useDispatch } from '../utils/redux-utils.js';
+import { useSelector } from '../utils/redux-utils.js';
 
 function useChildThreadInfosMap(): {
   +[id: string]: $ReadOnlyArray<ResolvedThreadInfo>,
@@ -243,10 +240,9 @@
   const keyserverCall = useKeyserverCall(changeThreadSettings);
   const updateFarcasterGroupNameAndDescription =
     useUpdateFarcasterGroupNameAndDescription();
-  const fetchFarcasterConversation = useFetchFarcasterConversation();
-  const fetchFarcasterMessages = useFetchFarcasterMessages();
-  const fetchUsersByFIDs = useGetCommFCUsersForFIDs();
-  const dispatch = useDispatch();
+  const modifyFarcasterMembership = useModifyFarcasterMembershipInput();
+  const refreshFarcasterConversation = useRefreshFarcasterConversation();
+  const auxUserStore = useSelector(state => state.auxUserStore);
 
   return React.useCallback(
     async (input: UseChangeThreadSettingsInput) =>
@@ -256,21 +252,19 @@
           processAndSendDMOperation,
           keyserverChangeThreadSettings: keyserverCall,
           updateFarcasterGroupNameAndDescription,
-          fetchFarcasterConversation,
-          fetchFarcasterMessages,
-          fetchUsersByFIDs,
-          dispatch,
+          modifyFarcasterMembership,
+          refreshFarcasterConversation,
+          auxUserStore,
         },
       ),
     [
-      fetchFarcasterConversation,
+      auxUserStore,
       keyserverCall,
+      modifyFarcasterMembership,
       processAndSendDMOperation,
+      refreshFarcasterConversation,
       updateFarcasterGroupNameAndDescription,
       viewerID,
-      fetchFarcasterMessages,
-      fetchUsersByFIDs,
-      dispatch,
     ],
   );
 }
diff --git a/lib/shared/threads/protocols/farcaster-thread-protocol.js b/lib/shared/threads/protocols/farcaster-thread-protocol.js
--- a/lib/shared/threads/protocols/farcaster-thread-protocol.js
+++ b/lib/shared/threads/protocols/farcaster-thread-protocol.js
@@ -46,19 +46,13 @@
   ThreadJoinPayload,
 } from '../../../types/thread-types.js';
 import { updateTypes } from '../../../types/update-types-enum.js';
-import { type ThreadUpdateInfo } from '../../../types/update-types.js';
-import { extractFarcasterIDsFromPayload } from '../../../utils/conversion-utils.js';
-import { convertFarcasterMessageToCommMessages } from '../../../utils/convert-farcaster-message-to-comm-messages.js';
-import { createFarcasterRawThreadInfo } from '../../../utils/create-farcaster-raw-thread-info.js';
 import { farcasterThreadIDRegExp } from '../../../utils/validation-utils.js';
 import { generatePendingThreadColor } from '../../color-utils.js';
 import { type ModifyFarcasterMembershipInput } from '../../farcaster/farcaster-api.js';
-import { farcasterMessageValidator } from '../../farcaster/farcaster-messages-types.js';
 import {
   conversationIDFromFarcasterThreadID,
   extractFIDFromUserID,
   farcasterThreadIDFromConversationID,
-  userIDFromFID,
 } from '../../id-utils.js';
 import { messageNotifyTypes } from '../../messages/message-spec.js';
 import {
@@ -157,10 +151,9 @@
     } = protocolInput;
     const {
       updateFarcasterGroupNameAndDescription,
-      fetchFarcasterConversation,
-      fetchFarcasterMessages,
-      fetchUsersByFIDs,
-      dispatch,
+      modifyFarcasterMembership,
+      refreshFarcasterConversation,
+      auxUserStore,
     } = utils;
     invariant(
       !changes.color,
@@ -190,58 +183,40 @@
       );
     }
     if (changes.newMemberIDs) {
-      throw new Error('newMemberIDs not implemented yet');
+      const targetFids = changes.newMemberIDs
+        .map(memberID => {
+          const targetFid =
+            auxUserStore.auxUserInfos[memberID]?.fid ??
+            extractFIDFromUserID(memberID);
+          return targetFid ? parseInt(targetFid, 10) : null;
+        })
+        .filter(Boolean);
+
+      if (targetFids.length > 0) {
+        const modifyFarcasterMembershipInput: ModifyFarcasterMembershipInput = {
+          conversationId,
+          action: 'add',
+          targetFids,
+        };
+
+        promises.push(
+          modifyFarcasterMembership(modifyFarcasterMembershipInput),
+        );
+      }
     }
     if (changes.avatar) {
       throw new Error('avatar not implemented yet');
     }
 
-    // Perform all updates before fetching updated thread
+    // Perform all updates before refreshing conversation
     await Promise.all(promises);
 
-    const updatedConversation = await fetchFarcasterConversation({
-      conversationId,
-    });
-
-    const update = ({
-      type: updateTypes.UPDATE_THREAD,
-      id: threadInfo.id,
-      time: Date.now(),
-      threadInfo: createFarcasterRawThreadInfo(
-        updatedConversation.result.conversation,
-      ),
-    }: ThreadUpdateInfo);
-
-    const messagesResponse = await fetchFarcasterMessages({
-      conversationId,
-    });
-    const farcasterMessages = messagesResponse.result.messages;
-    const userFIDs = farcasterMessages.flatMap(message =>
-      extractFarcasterIDsFromPayload(farcasterMessageValidator, message),
-    );
-
-    const fcUserInfos = await fetchUsersByFIDs(userFIDs);
-
-    const newMessageInfos = farcasterMessages.flatMap(farcasterMessage =>
-      convertFarcasterMessageToCommMessages(farcasterMessage, fcUserInfos),
-    );
-
-    if (fcUserInfos.size > 0) {
-      const newUserIDs = Array.from(fcUserInfos.entries()).map(
-        ([fid, user]) => user?.userID ?? userIDFromFID(fid),
-      );
-      dispatch({
-        // TODO: importing processNewUserIDsActionType causes circular
-        // dependencies that are hard to resolve
-        type: 'PROCESS_NEW_USER_IDS',
-        payload: { userIDs: newUserIDs },
-      });
-    }
+    await refreshFarcasterConversation(conversationId);
 
     return ({
       threadID: threadInfo.id,
-      updatesResult: { newUpdates: [update] },
-      newMessageInfos,
+      updatesResult: { newUpdates: [] },
+      newMessageInfos: [],
     }: ChangeThreadSettingsPayload);
   },
 
diff --git a/lib/shared/threads/thread-spec.js b/lib/shared/threads/thread-spec.js
--- a/lib/shared/threads/thread-spec.js
+++ b/lib/shared/threads/thread-spec.js
@@ -24,7 +24,6 @@
   LeaveThreadResult,
   RemoveUsersFromThreadInput,
 } from '../../hooks/thread-hooks.js';
-import type { GetCommFCUsersForFIDs } from '../../hooks/user-identities-hooks.js';
 import type { RolePermissionBlobs } from '../../permissions/thread-permissions.js';
 import type { ProcessOutboundP2PMessagesResult } from '../../tunnelbroker/peer-to-peer-context.js';
 import type { TunnelbrokerSocketState } from '../../tunnelbroker/tunnelbroker-context.js';
@@ -88,13 +87,9 @@
   OutboundDMOperationSpecification,
 } from '../dm-ops/dm-op-types.js';
 import type {
-  FetchFarcasterConversationResult,
   SendFarcasterMessageResult,
   SendFarcasterTextMessageInput,
   UpdateFarcasterGroupNameAndDescriptionInput,
-  FetchFarcasterConversationInput,
-  FetchFarcasterMessageInput,
-  FetchFarcasterMessageResult,
   UpdateFarcasterSubscriptionInput,
   StreamFarcasterDirectCastReadInput,
   MarkFarcasterDirectCastUnreadInput,
@@ -167,10 +162,11 @@
   +processAndSendDMOperation: OutboundDMOperationSpecification => Promise<void>,
   +keyserverChangeThreadSettings: UpdateThreadRequest => Promise<ChangeThreadSettingsPayload>,
   +updateFarcasterGroupNameAndDescription: UpdateFarcasterGroupNameAndDescriptionInput => Promise<void>,
-  +fetchFarcasterConversation: FetchFarcasterConversationInput => Promise<FetchFarcasterConversationResult>,
-  +fetchFarcasterMessages: FetchFarcasterMessageInput => Promise<FetchFarcasterMessageResult>,
-  +fetchUsersByFIDs: GetCommFCUsersForFIDs,
-  +dispatch: Dispatch,
+  +modifyFarcasterMembership: (
+    input: ModifyFarcasterMembershipInput,
+  ) => Promise<void>,
+  +refreshFarcasterConversation: (conversationId: string) => Promise<mixed>,
+  +auxUserStore: AuxUserStore,
 };
 
 export type ProtocolCreateEntryInput = {