Let’s apply your friend’s logic elsewhere. If all statements made by the Church in the present tense are, ipso facto, mutable, this also means that the Church can authorize divorce! After all, the priest says, "I now pronounce you man and wife" (present tense). So who says the happy couple is still married five minutes from now? "This is my body" is spoken in the present tense. So there’s no guarantee it stays Christ’s body after the act of consecration. Going further, the whole Creed is up for grabs by your friend’s lights. After all, "we believe [present tense] in one God . . ." Who says the Church will believe that next year?
Indeed, if we accept your friend’s reasoning, atheism is now potentially compatible with Catholic belief! After all, God is I AM (present tense). Who knows if he will still exist five minutes from now?
Your friend’s is perhaps the weakest argument against the authority of Ordinatio Sacerdotalis I have ever encountered.