Downgrading question

[sinnerchrno]

For the 3gs how exactly does the signature thing work? If your phone was already pwned does it mean that the firmware still needs to be signed when restoring whether or not it's custom? Or would it work if i downgrade from 3.1 -> 3.0 using a custom firmware?

[L00i3]

Is there a way to get a custom 3.0? After all the research I have done on the 3G[S], I still have never heard of a custom 3.0 for 3G[S]. I would like to make myself one though, if there is in fact a way.