I had a dream last night...

[fungus]

Someone had found a way to downgrade 2.6.

Sony had released 2.61, someone used that update, gutted out all of the information, except for something to do with confirming that it was for 2.61, and replaced all of the update info for that of 2.0. The guy that made it said that your PSP will think its at 2.61, but in reality it is really running on 2.0. It was just tricking it into thinking it was a newer version, where really it wasnt.

Go ahead and laugh now.

[iniquitous_beast]

I once thought that I could put my mind into a live gorilla. I just had to cut out all the parts of his brain that controlled gorilla-thoughts, and leave in the necessary stuff that controls heartbeat, etc. Then, I would replace the parts it took out with pieces of my own brain. Voilla! a talking gorilla!
Alas, it didn't work. My gorilla has never been the same since that fateful day.

The moral of this sad story is that sometimes a good idea is only a good idea until someone tries it. Sadly, this good idea that you have suggested has already been tried in the past when sony upgraded previous firmware versions.
Like a gorilla's brain, firmware versions can not be easily cut up, pieced haphazardly together, and thrown back into the psp. They are very complex.

To date, nobody has succeeded in reflashing their psp with a self-made (read: meat-collage) firmware. Keep thinking, though. You never know when you'll stumble upon a new idea (that works).