I try no matter what to keep consistent pressure. To me if you focus on applying varied amounts of pressure it will lead to inconsistency in angles. By principle it makes sense and I think it is natural to apply more pressure in this manner but it is only something I think about with de-burring.
I don't really change the amount of pressure too much. At least not concsiously... I don't use a lot of pressure to begin with, though. Jon recently told me to sharpen like I meant it when I was trying out a stone, haha. I told him that's how I always sharpen and especially light on the finishing stones.
Not every time, and not consistently within a session. It's not a critical thing, methinks. It did help me to speed up when I was newer, but it required a bit more focus to maintain the angle. Obviously, it wears the stone unevenly, so keep that in mind.