Hey Christian. Good questions.

So I often paint over models. But when I do, I am painting just paint on paint. Remember, you should undercoat/basecoat a mini and you can paint as many times as you want. You should use think coats of paint.

When an old model was painted with this coats of paint, then you can paint over it. But when it is painted thickly, it becomes necessary to strip the paint off. You need to be careful with the method you use and they type of model it is, but all the paint comes off for Clean Green and everything except resin finecast models are usually fine in it.

I will be showing this in a post soon!