I had a spare Ratchet from some two-pack that I tried soaking in cold dye months ago, to no effect. I finally got around to trying my double boiler bath, and it worked pretty well, giving me a base red color that would make any unpainted seams blend in. I carved off the existing crest and fabricated my own, carved off some of the chin, moved the mouth down and filled in the vents on the helmet. Otherwise, the only physical mod was adding a chest crest. It does transform, although not as springily now that paint is in some of the joints. :) And, of course, there's issues with dye soaking through the paint, requiring more coats than usual. The speakers are deliberately wobbly, like in Soundwave's animation model (if not on his toy).
I spent about two weeks working on this, taking it really slow to avoid paint getting sloughed off because I was impatient.