What steps did I take?
1. Take my 3.02OE-B psp and sacrifice it
2. Use the recovery flasher and the official 2.71 EBOOT to get back to standard Sony 2.71 and check system settings to confirm it worked.
3. Use the official Sony updater to updat to 2.80 and check system settings to confirm it's now really 2.80
4. Format the memorystick on the 2.80 firmware psp.
5. Move the 2.71 extracted DATA.PSAR and Psardumper to the memorystick.
6. Use my other 3.02OE-B psp to extract the DATA.PSAR to F0
7. Add 0okm's files to the memorystick
8. Install eLoader 0.995
9. Start xLoader (NOT eLoader!) after a few tries and a custom background.
10. Start 0okm's downdater straight from the XMB, thanks to xLoader.
11. Cross fingers and wait... It didn't take long at all, maybe 30 secs or so.
12. Confirm the almost obligatory BSOD with 'O' and restart.
13. Check system settings, firmware is now 2.71 again.
14. Use HEN-D and the generic downgrader to downgrade to 1.50 so I can install 3.02OE-B again

I had a UP ready to install in case I'd brick my psp but I didn't need it

someone leaked and more than 200 email req. it

so

if you know HowTo use and can take the Risk
and Accept NOT share it to other people
you can Download it

Download-Link #1: FW280DownDate2FW271.zip
Download-Link #2: FW280DownDate2FW271.zip