In T156584, many extensions were made compatible with MediaWiki-extensions-UserMerge. There's also MediaWiki-extensions-Renameuser 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-extensions-Renameuser triggers RenameUserSQL hook.
Examples of complete support: