I know if the mistake is objectively reasonable, any evidence obtained in a search pursuant to an otherwise legal warrant (i.e. building schematics show that a second story is a one-unit dwelling, but it turns out there are two - and the police go into the wrong one - as in Maryland v. Garrison, 1987 Supreme Court case). I just wondered if you could be prosecuted for firing on police (supposing you weren't obliterated in the process) in the same type of instance.
For now, I will just do my best to check to see if they are cops - if they are not (i.e. it is a BG yelling that he is a cop in order to get me to drop my defenses), I hope I can tell the difference quickly!