I didn't see your post until now. Yes, I used to do that in the early 80s when the only Satin Black was a hard to find Humbrol Shade or one of the aircraft color line by the defunct Pactra, called either Aircraft Black or Radome Black. Otherwise, for radomes and such, I either mixed gloss and flat black, which was best, or gloss and flat clear, which was an unwanted one more fat coat of paint to hide detail, and just wasn't and isn't as satisfying, and I use that method in a pinch even now. I miss some of those old Pactra paints, especially the Anti-Glare Panel Green. It was perfect for 1950s aircraft (the real color is Medium Green Flat, but Pactra sunbleached it, which it was).
Speaking of mixing, I matched the commercial shades of RLM 66 scwarzgrau (black-gray) for cockpits and such, against the chips in the Monogram Publishing Official Painting Guide to the Luftwaffe, and I found that the commercial shades were all too light, even accounting for scale lightening. So I mixed 50-50 MM black and Gunship Gray, and guess what? A perfect match with a tiny lightening for scale, and so all that detail won't vanish in the blackness. It's also good for tires, with a dry brush of lighter tire gray on the part where the rubber meets the road.
Tom