D.D.
My Dad spent a couple weeks with us there using his Yamaha 1000 with zero problems and no re-jetting. Don't think the rich mix will hurt a thing. Now if you did re-jet for the higher altitude and then continued to run it when back down to the lower places, that lean mix could be really bad news for the generator. Personally though, we have had a Honda EU 2000 since 2007 and never used it in Yellowstone. Don't like the darn noisy things unless there's a real need.
Yes, the fuel injected outboards do adjust automatically to the elevation, so no fouling problems, but without a blower to equal out the loss of oxygen there's going to be a approximately 24% power loss.
One is supposed to have permits for anchoring out and they can be hard to come by in mid summer, but there are ways around it. We hope to put the Hunkydory into the Bridge Bay Marina somewhere around the first of August to the end of the season and spend a good part of our time there, so will likely be about when you arrive. Would gladly PM you my cell phone number if you want. Yellowstone John should be around the lake most of the summer and I don't know anyone with more knowledge of the lake and its immediate surroundings them him. Between the two of us should be able to get you a leg up on your Yellowstone Adventure. Will be looking forward to meeting you there.
Jay