In T156584, many extensions were made compatible with MediaWiki-extensions-UserMerge. There's also MediaWiki-User-rename which supports extensions, too. All extensions should be updated to be compatible with both extensions.

Both extensions trigger a hook and other extensions can add their database tables and fields with user identifiers which should be updated.
MediaWiki-extensions-UserMerge triggers UserMergeAccountFields hook. MediaWiki-User-rename triggers RenameUserSQL hook.

• UserMerge-compatible extensions
• RenameUser-compatible extensions

Examples of complete support:

• CheckUser
• CodeReview