What are his chances at the Court of Appeals?
Very slim.
We don't have much jurisprudence on the matter, since prosecution under Art. 133 is pretty unusual.
The only defense I can think of is that his acts may be offensive to the feelings of the faithful, but cannot be considered "notoriously offensive," which is a strict requirement of the provision.
In 1939, SC Justice Jose P. Laurel once wrote in a dissenting opinion:
"...I believe that an act, in order to be considered as notoriously offensive to the religious feelings, must be one directed against religious practice or dogma or ritual for the purpose of ridicule; the offender, for instance, mocks, scoffs at or attempts to damage an object of religious veneration; it must be abusive, insulting and obnoxious (Viada, Comentarios al Codigo Penal, 707, 708; vide also Pacheco, Codigo Penal, p. 359)." Following J. Laurel's view, Celdran's act was directed against abusive members of the clergy, not specifically against Catholic dogma or ritual for the purpose of ridicule; hence not "notoriously offensive."
But still, malabo pa rin ang acquittal.