The modification is based on skipping two steps in the upgrade process.
"BD FIRMWARE" and "Bul-ray Disc Player Revoke list."
Here are ISO batch tools that permit to fully created your personalised ISO disc.
It's the easy way I found to do it. You will find multiple...
PlayStation 3 CFW Utilities
(Click Titles below for Information)
PS3 NET Server / GUI.
PS3 GamePad Test...
Separate names with a comma.