That is the nature of satin, it eventually glosses up a little bit. I've buffed up satin guitars to a low sheen finish. It's easy. Just polish it up with swirl remover. The first round I attached a buffing mushroom to a drill. The crevasses and hard angles did it by hand. Of course, if you're not gentle you could mess it up, but it's like that will all things, ain't it? Also, it's a pretty strange satin that doesn't gloss up some after years of playing. I suppose it all depends on your touch and your sweat.
Going the other way to increase the satin I think you'd have to repaint it.