Range- You change draw in 1/2" steps with the interchangable modules. I think Merlin has 3 different sizes of the Omega cams to cover certain draw ranges. Setting the adjustable peg on the Omega is for whatever particular module you have on the bow. Like for the 27.5" module I had on the bow the peg was in one position, but when I installed the 27" module I had to put the peg in a different position. The instruction sheet details where things should go for which modules and which version of Omega.

For the between module draw lengths, I assumed it was just done by string/cable twisting and untwisting. As long as the cables are in the tuning marks for your setup, things should be fine. This is different than Darton where you have 1/8" pegs on the cam that give 1" draw adjustment.