Never had FO morph in MP. However, if it has any vanilla in it may affect the colors; hence the use of Vanilla Color Stabilizer.
Add the same amount of stabilizer as FO. I have only found the stabilizer on-line.
Also, regarding shrinking, I have never had any of mine shrink. However, I do wrap in plastic wrap after they are set, usually wait overnight and wrap in the morning. MP is prone to glycerin dew and the plastic wrap helps keep out the moist air.
Also, if you haven't already, might i suggest you check out SoapQueen and Bramble berry (learn section). I learned a lot reading through her step by step recipes.