could you not use a proxy server to downgrade the ps3 by logging the system update url and adding an older firmware to it?
No, once the PUP tries to run, it also checks the firmware version, so it does not work.
Take the zeus.dl link of a file on psn (free)
Downloaded a pkg
Open PS3 Proxy
after configuration go in replace files
in the left paste the zeus.dl link
in the right select the pkg on your hd
go to the psn
select the file of the link on the left
when the download is finish,install and you found the pkg on the right
Sorry but english is not my language u can't understand good my tutorial