Hiya....
I have the Chaos War Mammoth, so I know you want to be careful with it.
I found this on the web....
http://reviews.ebay.com/Stripping-Paint-off-Model-Kits-Plastic-or-Resin_W0QQugidZ10000000001396152?ssPageName=BUYGD:CAT:-1:LISTINGS:6
and this...
http://www.armorcast.com/WorkingResin.html
and this quote:
To strip a RESIN KIT I use DEEP DOWN STAIN STRIPPER. I found it at Home Depot in the paint section, it comes in a red spray can. It is used for stripping the stain and varnish off of wooden items. On resin, it starts to work almost immediately and NO FUMES. I haven\'t tried it on vinyl yet, so you\'re on your own there. But for resin, it\'s teriffic!
BUT...I have not tried any of these myself, so I can\'t vouch for the effectiveness....
Maybe just try a small area, or another painted resin (cheaper one) first?