Possible to Downgrade TA-082's?
I've been thinking about this for a bit, and I think I've figured out a way to downgrade 2.6/2.71 TA-082's. What you would need to do is put harleyg's redovery mod into the flash of the 1.5 downdater file that you're using to downgrade; it should be something called recovery.elf that you put into kd folder. Once you have that in place, you will most likely be able to try downgrading from whatever downgrader you use, and get bricked. With harleyg's recovery mod, you should hard reboot, and turn on the PSP with 'hold' on, which should get you into a blue menu. If you don't already have the 2.0 update in your PSP/GAME folder, then select USB in the blue menu and you should be able to put the update in there. After it's in, click on Recovery Menu, and from there go to Start update EBOOT. You should be upgraded to 2.0, and from there you will probably be able to downgrade to 1.5.
DISCLAIMER: This is currently under speculation and may or may not work for your PSP. I accept no responsibility for any loss or damage caused by this information and/or instruction. I haven't tested this, because I myself don't own a TA-082 OR a 2.71. Therefore, I am not responsible for any bricks from attempts of this.