Laser printer paper for clear wall decals? Never done anything like this and not sure what to buy
Depends on the type of paint on the walls and the type of adhesive on the decals.  In general, with normal PVA the sticker is going to end up damaging the paint either by bonding tightly and peeling it from the wall when you remove the sticker, or reacting with the paint and discolouring it over time.
Some types of high gloss enamels fare better, but in general a sticker on the wall is going to have to stay there until you decide to repaint, otherwise there will be a mark.
Paint also discolours with age due to exposure to air and sunlight. So even if you find a miracle adhesive that doesn't do anything to the paint, it will then instead protect the spot under it and once you remove the sticker there will be a noticable spot on the wall that doesn't match the colour of the rest of the wall.
That said, most clear printable sticker paper and waterslide available are for inkjets rather than laser printers.  However, Silhouette America makes a &quot;printable clear sticker paper&quot; that is supposedly laser printable. I have not used it myself, but you can order it from Amazon