Your test subject might get some random events the second time around that are different from the first. Random being by definition not controllable by the copy paste. The uninverse is weird.
Well we can't be sure of that, or at least I certainly can't with my poor knowledge of space, quantum and so on... But let's say I make it so everything is the same for the whole time, except I don't force anything on my test subject, only everything else (until they make something different by themself, if that happens).