I don't see too many problem here.
1) let them install alarm system, but tell them to remove it when they move out.
2)They could replace all the lights, and put the original back when they move out.
3)They could repaint the room, but have to repaint back when they move out.
The rule is what you rent them is what you get back. You don't need to pay anything extract, only maintain what you rent them.