That would never happen. He is ordained in the Ukrainian Rite, not the Latin Rite. Even if he were bi-ritual, he remains Ukrainian Catholic.
Would a Greek Orthodox priest ever apply to the Russian Orthodox Church? I believe this is the same thing. Maronite is Maronite, etc.
NYer, I remember reading about a ROCOR priest who became a Melkite Catholic priest. Did you ever hear about that? I may be completely wrong on this. I can't find anything about it now.