Does nocking point change ?
For me, the nocking point is located where I get level flight from a bare shaft. My understanding is that usually the nocking point for 3 under is higher than the nocking point for split. So if I were changing from 3 under to split, I would initially choose a nocking point 1/8" lower than my nocking point for 3 under. But then I would shoot a bare shaft and would no doubt need to make further corrections.
Most folks use a higher nock point for 3-under. Helps to equalize limb flex and quiet the bow a little. So, yes, if you go from 3-under to split, you will probably want to lower your nock point a little.