Short answer, no.
Somehow A:M would have to have to be storing a keyframe unchanged even after you change it.
For how long? A keyframe on a character might involve many bones. At what point does the software decide that "the way it is now" is the the thing it needs to save that you might want to come back to? I don't see a practical way to do that.
I do save many many versions of my work as I progress. in a desperate pinch it is possible to reload an old chor, copy a keyframe from it and paste it onto the new chor.