Can the Transfer Funds form be customized?
Straight nope. Not possible. I’ve asked support about this a number of times. I can’t tell whether it’s because they just built it that way and are too lazy to change it or they’re afraid someone will break something related to currency translation that they won’t be able to sort out.
Just do a journal entry with a custom form restricted to certain users or whatever, and do whatever workflows, scripting, etc. you need to do there.