Is there a skill to changing characters fast on Resident Evil 0

There's actually two ways you can do this. You can either go to the status screen and press X or during the game, just press X. That's really all you can do. Remember, try to use the other character to your advantage. Sometimes you can't solve a puzzle without your partner. Try to figure out when your partner could really be helpful. Luckily throughout the game, you will see that you do in fact need your other partner's help. Obviously you can see that I'm not pointing fingers at anybody such as Rebecca or Billy. That's because I don't want to confuse you. But, hopefully you understand what I'm saying.