Hi! While working on minime, which comes with an on-the-fly character selector since the past few weeks, I noticed that my invincible character got attacked when I switched over to a new one. I've fixed that for my next release by copying character.destructible from the old character. However, I believe this is something that you also should fix on your end because my mod isn't the only one around that allows players to change their appearance, and it's quite confusing if your character gets killed although it's still supposed to be invincible according to your GUI.
I don't think there's an easy solution, as far as I know there's no event that would trigger when a player's character changes. It's different if you turn off your character altogether (God mode), but that doesn't apply in this case. I've added a custom event that I raise when the old character has been detached from the player (it still exists at that point) and the new one has been created and assigned to the player. (But that's of no concern to you as I've already fixed my mod.) Other mods may do something similar, but of course you'd have to know about them. It would be great if you could figure out a way to notice if a player uses another character even though it should be the other mods' responsibility to clean up behind themselves. (You can't trust that others will do that, or will even know that there may be an issue at all.)