There is no way either to downgrade from such a version, however, there have been some reports (perhaps some are fake) of some people reporting succesfull attempts at passing the initial barrier of the 2.0 version but there is not any software to prove it yet.

I’d say it’s only a matter of time. Anyway, back to the subject, if you have 1.0 firmware upgrade to 1.5, there’s no problem in doing since you can run homebrew and most of the latest releases are made to run on 1.5 anyway. In case you don’t want to, and this emulator isn’t compatible with 1.0 download Sei’s PSP Tool and try to use it’s “Export to 1.0″ option when installing the program.