It was in the list.
I didn't have time to work on the wiki page yet to create the homebrew descriptions, but I try to keep the homebrew list as complete as possible, it will be easier to find a program's name to create the homebrew's page later.
It's "xReg plus", by Cyberskunk.
It can backup and restore your xRegistry.sys file to/from USB.
It can also reactivate the licenses from your legally purchased DLC.
The reactivation is only temporary, so you need to run this homebrew and reactivate every time you want to play a DLC.
http://rebug.me/?p=304
A screenshot can be seen here :
http://www.ps3-addict.fr/forum/xreg-plus-1-0-t2419.html
You must have a backup of your act.dat from your first/old HDD.
Your new HDD must already have the exdata folder created (dev_hdd0/home/000000xx/exdata/).
1. Place your act.dat at the root of your FAT32 device, and connect it to USB000 (The rightmost port, near the disc reader).
2. Launch xRegPlus and press O to copy the act.dat into you xRegistry's USRDIR folder so you don't need to keep your USB connected (dev_hdd0/GAME/XREG00001/USRDIR/act.dat).
(or you can use a file manager to place it here)
3. Now every time you want to activate your DLC, run xReg Plus, and press X.