You could flash the firmware a thousands times, and the console ID will stay the same. As l3allermann82 says, one console has one console ID, the only way it's gonna change is if you change it yourself on a custom firmware, or with an E3 flasher. (not sure if you can even flash a CID with a hardware flasher. It seems like something that could be done, though...)
And you're not gonna get any console IDs around here. It's explained why in various posts on the site, but to put it simply: when you buy a so called 'private' CID, chances are that ID will have been sold to many other people, meaning somebody else will get that ID banned through doing something silly. Though, it only takes two consoles with the same CID to be signed in to PSN simultaneously to get that ID banned, so you may not even have a chance to do something stupid...
The only 'safe' way to unban your console is to get a broken console, and extract the CID from a flash dump from said PS3. Though, even this is risky, as the previous owner could have taken the CID to sell on or re use himself when he's been a silly-beggar and used his mods too much online.
So, basically, you're fooked. Sorry dude.
P.S. There are probably a sea of grammatical errors in this post, I haven't slept in about 43 hours. =D