This will depend on what kind of decals. The decals made by the Lego group is quite easy yo remove and you can do that with your nails. But custom decals are tricky. Most of the time they are perm, so you will have to get a scraping tool to get it off, therefore, damaging your Lego. That's why custom decals are discouraged by traditionalist.
I wouldn't risk putting paint over any decals. In general, it must be quite easy to remove decals first.
Yes, It is possible to remove window decals for cars. You can buy a kit for cheap on how to remove it properly so you do not scratch your window or even ruin the decal too.
use a heat gun (wagner heatgun)
Wall Decals are easy to remove and do not leave a sticky residue. There may be some minor paint coming off which can be easily repaired with minor paint touch ups.
If you mean back decals then use alcohol.
When customizing your bike frame with decals, consider high-quality vinyl decals that are durable and weather-resistant. Look for decals that match your style and personality, and make sure they are easy to apply and remove if needed. Popular options include custom designs, reflective decals for safety, and brands like 3M or Oracal for reliable quality.
Obama Decals, Storm Decals, Jean Grey Decals, and Wolverine Evolution decals Plz!
scrape it with a blade and then use alcohol to remove the sticky stuff.
Goo Gone will remove it
There really isn't a way to remove a paint thinner stain from wood furniture. You must repaint or re-stain the furniture.
With skills.