Unfortunately I think you’re going to have noise issues when you switch between guitars. Picture what it sounds like if you just yank the cord while the amp is on and unmuted. Here is a product off the shelf that does the reverse of what you want to do—it switches one guitar between multiple amps. They claim that they had to use some sort of active pop suppression scheme to prevent this kind of noise. Unfortunately I’m not sure there’s a simple way to DIY what you’re trying to do unless you can either implement that type of pop suppression, or tap into a mute function on your amp that mutes during the switchover event. (By the way, if you figure it out then please report back! I could use something like that myself.)