So after some trial and error I got it to work. These are the steps to reuse the prize boxes via flash drive.
Step 1:Unlock several prize boxes online and do not use them.
Step 2:After you have the desired amount, take your profile to your computer and create a copy of it on your desktop.
Step 3:Unplug your console from Xbox live.
Step 4:Power up gears and spend all of your prize boxes in a row, without returning to the gears menu.
Step 5:After you spend the final box, click A to dismiss the reward and unplug the flash drive containing your profile.
Step 6:Sign out of your Xbox profile.
Step 7:On your computer put the copy profile you made into horizon and save it to your flash drive overwriting the old one.
Step 8:Plug the flash drive back into your Xbox.
Step 9:Sign back in.
Step 10: Press start, go into the game and unlock more stuff.
Step 11: Repeat.
After you have everything you want, do it again and after step 4 just back out of the rewards menu to the gears main menu and it will save to your profile. Just bring that profile back online and everything will be unlocked.
The game will keep the unlocks each time so they just stack up. Worked for me just fine, let me know what happens for you guys.