Asian PSP 1.51 is possible to to downgrade 1.5 japnese ROM

I have PSP asian 1.51 is that possible to me to first upgrade to 2.0 JAP & than downgrade to 1.5 JAP. I read all proses I just want to no that in Asian PSP japnese ROM working without any problem or will problem for me.

One thing more I think to buy 2.0GB memory stick to run the games like burnout legend or etc. any advice

Yes other firmwares work. If you are buying the 2.0 gig for free games then that ilegal. Isos are only legal if you own the game first. I don't think you really need a 2 gb. a 1 gb is fine