Success!!

I just upgraded to 3.55, downloaded and activated my psn dlc, then downgraded to 3.41, and reactivated my dlc.

Here's what i did.
After downloading and activating my psn content, i made a complete backup of my ps3 through ftp this included hdd and flash.
Then i downgraded to 3.41.
I made a user with the same name as my backup.
I copied to my ps3, my entire home folder, my xregistry files, and my game folder.
After restarting, xregistry was rebuilt, i copied this back over.
After the next restart my xregistry was back to it's backup.
I forced the ps3 to rebuild its databse, by replacing, the mms folder with my backup. This froze my ps3, and the database was rebuilt. You could probably do this with the option in the recovery menu.
This rebuild made the ps3 recognise all my save games, and dlc.
I then put the act.dat, where it belongs, as it got removed again.
I now have all my dlc on 3.41, activated.
I'm pretty sure i got all neccessary steps. Have fun.
I should mention this was a slim, so some steps may change for a phat model. Also, you will need to replace the act.dat every boot, just like the method in this thread.