When we do Kaparos, we say "this money shall go to charity" -- so I put that dollar bill in the tzedaka box; is it okay if a few days from now I count what's in my tzedaka box, write a check for the equivalent and mail it to my favorite charity, and then put the dollar bill back in my pocket? How directly "to charity" does it need to be?
Normally I'd assume tzedaka money is fully fungible, but this one is part of a somewhat-spooky ritual, so I thought I'd ask. Perhaps since we say, "This is my exchange; this is my substitute; this is my atonement.", we must give this specific money to charity.