There is a few other things I want to mention which you might have overlooked.
First of all, after you finish with the downgrading process, you can just format your memory stick to make it normal again.
Secondly, you have to return you battery to normal after finishing the downgrade or else it will always boot in service mode and that means you can't play any games. You should have an option before turning your battery into a Pandora battery to make a Dump of the battery's flash file so you can restore it later by running Pandora's battery creator and pressing L+R.
Also, after you finish with this process you will end up with a 1.5 FW PSP and you shouldn't leave it that way. You should upgrade from that 1.5 FW to 3.71 M33-4. Sadly its not as easy as just running a updater but I have a good link for you here.
And thats it. I hope everything goes well and you'll be having fun on your downgraded PSP.
I don't think those things apply to him. He has a slim PSP, so he can't downgrade to 1.5. The Newbieinstaller he'll be using will install 3.71 M33-2 or something I believe.
Also he's using a Datel Tool battery, so he won't need to restore anything, just insert his old battery again.
I didn't know that. Just trying to pass on what I learned 's all...