Originally posted by RainMaker.
Unfortunately yes you will lose them, i believe that it replaces what is on the 4.25 with what is currently on the 3.55 so if in fact you game shared, after you transfer instead of just signing back onto your account and re downloading the games like you normally would, you will need to re gameshare and sign back into others accounts. (i believe) unless you backup your system before you transfer then when you wish to play the game shared games just restore the back up? I think that would work too.
I found this on a forum, so I think you can just backup DLC: (this was a guy that asked if he can copy DLC to another hard drive with a backup)
Simple answer to this one. Yes!
You need a USB drive, formatted in FAT32. As long as all your DLC and other data is less than 32Gb (for reasons I won't go into, however big your drive is, the maximum that the PS3 will see it as is 32Gb). So, taking all that as being true, you plug in your USB drive. Then go to the settings menu in the XMB and go to the Backup Data option. Back up onto the USB drive. Put your new drive in. Let it format, then restore the backup data from your USB drive.
Everything will be intact. All user accounts. All DLC. All game saves. And all downloads.
The only possible problem will be if you have more than 32Gb of stuff. Then you'll have to delete some things and re-download them. But your DLC will be fine, and that would be the most painful to have to do again, as it is so many small files. At least if you have to delete GT5 or Warhawk or whatever, it's only a single download to get it back. And you can still keep your Game Saves for those games, so you should lose nothing by having to download them again.
It's really simple. Good luck!