Our chapel has a set of rose vestments that the priest didn't like, so on Gaudete Sunday, he ended up wearing purple instead. So after Mass, I offered to donate $1,500 towards a new set of rose vestments. He accepted. The next day, an announcement was made regarding an ecuмenical activity the church would be engaged in. Had I known about that activity, I would not have made the offer. But as it stands, the offer has been made and accepted.
What would John Wayne do? I know this is not a matter of sin/non-sin, but honor is the next most important thing to me. If a man doesn't have that, he doesn't have much. Would reneging now impact my honor?
No. An honorable Catholic would, upon realizing that this is not a Catholic Church, depart and never show his face there again. Donating money to a non-Catholic sect is not something a Catholic should do.
Oh, and you should explain to the person (I presume the priest) that you will never participate in his evil.
But, seriously, when you're part of the Novus Ordo sect, what on earth did you expect?