I this degreaser (oven cleaner) to remove paint. It did not do ANY damage to the original vinyl underneath. However, the conversion vinyl pulled the paint off the original vinyl in a rectangle. One pic is of the stuff I used, that I only found at K-Mart. The other pic is a 6 player x-man that was painted 100% black. I sprayed on, covered with a paper towel so it wouldn't drip off,(the wet towel stays fine on a verticle surface). 20 minutes later I EASILY scraped the old paint off. I use the plastic "spatulas" they sell for working with bondo. They don't scratch whats underneath. I think any plastic spatula will do. The orange stuff removes 100% of the paint, with NO damage to the vinyl. However, I don't know if it would have an effect if the origiinal art was painted on...
Steve