You need to be a little careful backing yourself into a particular "corner". I learnt with three fingers up because it was very comfortable - and that was the advice I received from the 1st Trumpet player from the Sydney Symphony Orchestra - my first tutor. It suited my trumpet, but more especially fitted my embouchure. As I have aged (notice I don't admit to growing up) my fingers have "filled out" because I have worked hard with my hands. Now I have changed trumpets a couple of times and the latest - a Getzen Eterna 900 - and my changing face and hands have determined that I need 2 up and 2 down, I can't actually fit any more fingers above the 3rd valve slide. This transition hurt the base of my fingers a lot, and for many months. This is normal transition from "best position" to "best position" for me - I didn't learn any oddball grips to 'spite' an old guy, or to prove anthing - so I didn't have to unlearn stuff per se. But I still had to change - and I suffered pain. Best of luck, be careful though - as you grow older you'll be amazed how much the old guys have learnt in the same time. I discovered how clever my Dad became - as I grew up, I don't know how he managed that little trick.