I move things around in my tank from time to time. In fact, I did a major move around yesterday and it was no big deal.
Seeing as everything in my tank (so far) is fake, it was just a minor annoyance because a good chunk of my arm got wet.
Other than that it's no worries. In fact, setting up all the plants before putting water in is kinda silly anyway since dumping water in can move them around a bit and they won't exactly sit right unless they're underwater like they're made to be.