ok just to confirm....
i unlock my flyer (wifi) with htc dev...i couldn't downgrade using this method. After i relock my bootloader (instruction for unlocking and relocking is on htc dev)
Now with relocked bootloader after multiply times i get my flyer downgraded from official honeycomb to official gingerbread (be sure u use right RUU for ur flyer!!)
I make a lot of mistakes most of them small unnoticeable, so just read through instruction and keep trying and u will get it. (in fact it took me 3 and half hour
IF U UNLOCKED WITH HTC DEV JUST RELOCK UR BOOTLOADER THIS METHOD WILL STILL WORK.
thank you "globatron" for this great solution u save my life.