I'm with Benny, we need more info to be able to help, i.e. why you want to move it that much ? Moving the top of the mast 4 to 6 inches will have a great impact on the handling of the boat. Are you sure that it is that far back ? Have you measured the distance between your main halyard hanging at deck level and the foot of the mast ? Type and brand of roller furler and perhaps a picture. This forum is great and you will get help but please you need to help us help you.
Add-on: 4-6 inches will probably be too much to be able to take in by tensioning a turn-buckle (if their is one) so you'll probably have to cut the forestay and install a Sta-Lok fitting. Might mean shortening one of the extrusions of the furler as well. And will you have enough back-stay length to allow you to move that much forward ?