I learned the grip change/catch by jumping to HS from a mini tramp under the bar (and doing the hop), which makes it a lot easier. But after that, getting over just took trying it a bunch of times to get the timing. I always did it on the low bar though into a pirouette. I think it would have been easier on the high bar because I cast better out of a long hang kip. But I never had a reason to do it on the high bar in any routine or anything.