PS3 Kiosk/Display model on 4.00 right now. Options?

Like the title says, I picked up a CECHA-series PS3, but it was previously a display model and it's currently on kiosk fw 4.00, meaning it's locked down and neutered to all hell. I know the system's hardware is identical to the regular CECHA series though, so it should be possible at the very least to install stock (retail/OFW) firmware so I can stop having to deal with a half-functional system and needing this damned password to access half the features that I DO have access to. I get that there's no "downgrade" solution via soft-modding, but I'm not uncomfortable cracking it open and getting my hands dirty if I have to, I just have no point of reference here and want to know what my options are. I've read that with my model, I've got a system was probably shipped with 1.0 or 1.5, I forget exactly which, and that it's got a NAND chip, meaning I need a progskeet if it comes down to hardware. Problem is, beyond knowing those words and names, I'm at a loss as to where to get them, how to use them, or what to do once I have done.

Ideally I'd like to get this back to 3.55 for the backups, homebrew, and CFW goodness I see so much about, although I'd be content just to get 4.00 OFW if I can, and might even try to jig it for dual-booting so I could still screw around online when I felt like it. Actually that's another question I had- I know I've read that 3.55 is totally locked from PSN, but does that mean no online multiplayer, etc. as well? I assume yes, but since I'm completely new to the PS3 scene I want to come in with no assumptions. Basically, if anybody could please tell me how I go about backing out from this kiosk-firmware crap to retail and, if possible, get back to 3.55 or older so I can do with it as I please.

Now as far as homebrew goes I generally know my way around Wii stuff, and once upon a time I kept up with PSP, so I'm not completely green as far as general terms and things like that go, but as far as resources and basic how-to's, I'm pretty lost. I know there's got to be plenty of great guides and such on this site already, but I literally just created this account for the above question, so I figured while I'm at it I'd ask anybody for recommendations for once I do manage to get this issue taken care of- what to do, what not to do, what the essential programs/packages are, etc.