i called my shop today and they said when you change the draw length it messes up your module, i dont understand what hes trying to say, is he saying youll have to buy new modules or what?

To go up or down 1/2" you will need new modules. To make small adjustments to the modules you have (with the draw stop peg) it will increase/decrease the amount of let-off you have.

Get as close as you can with the correct module and the adjust from there.