It is actually pretty easy. As long as you don't use any private APIs, you can completely change the behavior of your app after the review by changing server side settings.
It is partly an intent issue. If you are attempting to pull one over on Apple by hiding app behavior during review, well, they are not going to be happy about that.
Other folks are also noting that, because humans are sometimes bad at evaluating each others' intent, it is probably a good idea to attempt to make one's intent clear if going this route, lest you annoy the gatekeeper.