But if you want to use replace-by-fee to manipulate the amount of bitcoin sent, either to deduct from it or to add to it, or to use it to create two or more different transactions, it is not possible.
It is entirely possible to do all these things with RBF.An RBF transaction only had to spend at least one of the same inputs as the transaction it is replacing. It can add or remove other inputs freely, meaning you can absolutely send more or less bitcoin than in the original transaction. I can also use RBF to replace a transaction with multiple inputs, only include one of those inputs in my new transaction, and therefore free up the other inputs to be used in another transaction (or just left alone, if I want).
