Is there any way to safely put stickers on a MacBook Air 15"?

I’m not a fan of covers and cases. They can interfere with cooling trap dust. I’ve seen decals that claim to stick without glue. You might try searching “nonadhesive decals"

The case of the MacBook Air is a passive heat sink and if you cover it with stickers, it can overheat with product life-shortening implications and potentially void your warranty.

The plastic covers trap dirt like crazy which then grinds into the finish of the laptop damaging the finish. It acts like sandpaper. Plus some of those covers are so difficult to remove that you may even damage the Display from the pressure required to remove it (I make the user remove them so I am not accused of causing damage when repairing the laptop). And those plastic covers tend to crack which makes the one around the base loose. I've almost dropped several laptops because the laptop was slipping from the broken plastic case.

Many stickers are not easy to remove and can leave residue & marks on the laptop that may not be able to be removed. I have seen some people use vinyl cling stickers which are easier to remove, but I don't if they will damage the case. Definitely avoid putting anything on the Palmrests.