Христоса - not sure this form is generally used.

If you want the wording used in Russian religious texts (which would be correct in this case) you can say, "Хула на Христа есть хула на Митрополита Киевского" (хула is an archaic Russian word confined mostly to religious writings and speeches, it can imply 'affront' in this situation).

Митрополит is a title. (head priest, usually in a large metropolitan region and adjoining areas)