How do you actually set up the no peep? I don't understand the logistics of pulling your bow back to your anchor point, then lining up the no-peep, or exactly how it is done? Also, it sounds like the no-peep won't line up if there is anything changed in your set-up.
The No-Peep comes with full set up instructions.
Drawing the bow with your eyes closed 1/2 a dozen times to your anchor points.
Once you have done this install the No-Peep then draw the bow with your eyes closed to your anchor points then open your eyes adjust the No-Peep repeat as needed till everything lines up.
Do you have to change your no-peep each time you change something with your set up?
In short no but if you change out sights then you will have to re-align the No-Peep as the mounting bracket goes under your sight bracket.
Do you find that it is difficult to learn to use?
For the first couple of weeks you will probably go from looking at the No-Peep back to your sights but once you get used to it just a quick glance for reference is all you will probably do.
The one big thing that the No-Peep will do is give you a consistant anchor point and let you know if there is any touque or you if you have anchored in a different position.