Try adding this string to your Typemap:
binary+l //....uasset
That is a lockable designation. It means it’s read/write but also will be locked when modified in editor (when Source Control is connected) or when checked-out manually in P4V.
Since External Actors are just uassets, they can (and should) be treated by P4 the same as any other uasset you’re working with in your project.