And is this something that is worth doing i have a 4x4 flatbed and i am already doing a shackle flip so i will have the brackets already off and i just thought why not move it back .
Lets get back to why you thought of moving it back. What do you want to accomplish?
If you are going to install 56's (which I would because they flex better and ride better), the rear hanger will need moved back 4 inches no matter what. Running 56's, you have the option to install them backwards, this will push the axle back 4 inches.
If you are doing the home brewed shackle flip, you will want to test fit the rear hanger before fully installing it. You may need to adjust the hanger's placement to achieve a good shackle angle.
Oh, and which frame are you asking about? The Blazer runs 52's, your truck should have 56's already.