I teach a lot of pretty middling software developers about idempotence when discussing configuration management tools, and it seems pretty graspable. Idempotence is `f(f(x)) = f(x)` and nothing but. This is your #1.
Upon a second read, what AWS is saying is "if you pass a token and this has already been done with that token, return the original result." That token is just setting part of `x`.
Upon a second read, what AWS is saying is "if you pass a token and this has already been done with that token, return the original result." That token is just setting part of `x`.