I've done it on two different planes before. One was a Phaeton biplane that has the thrustline wrong and I didn't want to change it at the field. It would nose up (not just rise in altitude a little but genuinely nose up and continue to rotate until I adjusted the elevator) It took a little bit of tweaking to get the mix right but within one tank of fuel I had it right. I also did it on a foamy Stryker that had the opposite issue. I found that it did solve the trim issue when I stayed at a constant throttle, but the problem showed up with quick throttle changes. If I was going wide open in the biplane and let off the throttle, the plane would balloon up until it bled off some airspeed because of the mix. The opposite happened if I cruised around slow and then gunned it; the plane headed for the ground. The Stryker did the opposite, understandably so given that it had the opposite issue. I found that correcting for the mix was more trouble than just correcting the trim change anyway, but for a constant throttle flyer I suppose that would be far less of an issue. The right solution for me was to get the thrustline adjusted right for both models so that throttle changes wouldn't affect the pitch. The biplane still has a slight trim issue related to speed (which is a separate issue that is partly being a little nose heavy and the rest being in the design itself) but it is only maybe a 15-20 altitude change in maybe 600 feet of flying. The wind messes with me more than that, so it's ok.