Incorrect. Just look at a potential stub for this kind of function that I posted in a different thread.
The blocking function need only return originals of the functions it blocked. If that's not satisfactory, then just copy the references to the originating functions before blocking them. It's the same thing currently being done by modules wanting to deny other modules. The only difference is that there would be a way to do so provided by the engine, meaning it's no longer first come, first served. Instead, monkey patching and securing would be able to be handled separately.