The amount of movement you are able to get by moving engine back that tiny amount will be incidental, Since you feel it's a bit nose heavy don't be overly concerned. Fly it and then make any adjustments you feel are needed. If you have located your bat. pack back and find you do still need CG further rearward you can remove spinner, relocate elev, rudder servos all the way back to tail. I really doubt you will need this amount of adjustment. Fly it