I wouldn't lie about it. Fully denounce your faith. You can get it back when the threat is over. If it's still a threat, would you denounce it? Charity, though, doesn't have ties (I'm covered). It's the highest form of giving.
The reason I'm willing to lie about it, is because God knows our fragile nature of being humans and He knows what's in our hearts. Full belief rejection then getting back to it, I believe means that the full rejection was not real since telling you would get back to it means that you're still holding to your belief somewhere in your heart.