<< It may take a 27' ladder to get in there. >>
If you have no particular later use for a long ladder, rent one. Or if you
aren't comfortable at that ladder height, rent some scaffolding. A third
option, but pricier is to rent a ManLift, usually trailer mounted (need a tow
vehicle, of course).
<< I am guessing there may be a way to remove the gable vent and paint it and
put it back from the attic >>
I wouldn't bet much money on it, but have a look to be sure. HTH
Put some paint in a baggie and throw it at the vent.
Or do the logical thing, get your butt up there.