Max........if you want to remove it.......Devoe Coatings has a water based paint stripper called Hydro-Strip - it works very well. You should be able to find it at an ICI Paints Store - or a Devoe Paints Dealer.
Additionally - if you are going just the Gripper and paint route - use as flat a top coat as possible (if this room doesn't need to have washable walls) - that will make the lumpiness less apparent.