After having pretty much screwed up my Stormtroopers and ended up with too much paint that made them look like blobs of molten crayons I decided to strip them and just repaint.
The best tip I can give (that I got from Lukes APS on youtube so all credit to him!) is to use what is called "methylated spirits", in Sweden this is usually called "T-sprit" or "T-Röd", the latter a famous and common brand available just about everywhere.
The alcohol will not damage the plastic and will break down the acrylic paint in a matter of minutes!
This stormie was put into the alcohol for less then 5 minutes and then given a gentle brush with an old toothbrush and the paint just came right off of it! Give it a little more time and a better brushjob and the mini will look new and unpainted, large enough bowl and were talking de-painting several units and making them ready for new paint within an hour!
As always, working with chemicals and alcohols you should take care, use gloves and not spill the stuff around. The wastes alcohol is to be disposed at whatever local station you have available and while it doesnt give off a very strong smell, it is always adviced to work outdoors or in a ventilated area!
So there you go, a ruined paintjob isnt the end of the world!