Though it seems we're already discussing what to do AFTER the damage is done... Are there suggestions for ways to prevent it from happening when the labels are still intact and one wants to clean them?
Nail polish maybe? (will it dissolve the label's paint)?
Drawing Protective Lacquer (spray can)? Don't know what's the correct name for this in English... Here we find it in Design and Drawing stores, to apply over pencil drawn sketches, so they won't wipe or get smudged on handling. Will the lacquer stick well to the plastic and don't "lift" the labels?
What about removing the yellowish tint? The solution used by retro-computing and retro-gaming folks, of using 40Vol Hydrogen Peroxide + TAED (the oxygen activator present in OxiClean) + Sun Light... Will it wipe the labels or lift them?
To contribute with something, I have a spare button that is quite yellowish, and it still have its labels on it. I will try the Hydrogen Peroxide treatment and will post the results on the photos area.