I don't know any other way to change pinion angle without drilling new holes. If you are not getting a vibration @ steady 55-65 cruise in o/d, then I would not bother.
Lowering the car just helps a little in re- locating the already incorrect instant center location, to a bit more favorable point.
FWIW, The pinion angle is not a major tuning tool. It's something that helps reduce driveline bind, thus freeing up some HP to use where it's supposed to be.
There have been a bazzilion posts in ALOT of threads on this. I'd suggest a archive search, as it should give you some good info... and some "not so good"..