Can you paint a flat paint(PollyS enamel) over a gloss(Testors MM)....

…or do I need to flat coat the base color first?

Pat I’m not really sure what you are trying to achieve, are you talking about a coat for applying decals or a final coat or are you looking to achieve a particular finish? Regardless provided you give the MM gloss enough time to cure you can paint over it with the PollyS

Darren

Yes