Easy ways to add new animations to a model?

So, this isn't a problem I'm having yet, but I figure it will pop up eventually. At the moment, my player character has the basic animations--idle, walk, run, jump, attack. They're all on the animation timeline, separated into takes. But if, in the future, I end up needing other animations, like a death animation or an alternate attack, what would be the best way to go about adding those? Would I need to re-import the whole fbx model? Would that mess up my prefabs or scripts? Is there a way to import just the animation timeline and update that, or possibly import a set section of frames as a new take?