How can I paint over an existing paint design without making it permanent?
Some ideas


hang up fabric?
go to a large format printer (sign shop) and print banners and hang those?
get $10 shower panelling from Home Depot and tack those up on the wall (and paint on those)
don't bother with a 'theme' for the baby's room. I know a lot of people like to do it, but it's a lot of work, the kid doesn't really care, and they grow out of it really fast. That and for a lot of people, the baby ends up sleeping in the parents room anyways.