I've posted about similar attacks over and over again, and I still say don't let police into your house without a warrant.
In this particular attack, the police imposters forced their way into the home and spent twenty minutes robbing everyone at gunpoint. My thoughts on this are that if police are supposed to have a warrant to come breaking into your home, and if you are the kind of person who has nothing illegal in your home, or have done nothing to cause police to break down your door, then it is reasonable to treat anyone who breaks down your door as a deadly threat, regardless if they are in a uniform or not. Where I see a potential problem for the non-criminal home owner, like myself, is that it's not that uncommon for real cops to come busting into your home by accident or negligence.
The question then would be how would you be treated if you gunned down a state, local, or federal police officer that mistakenly picked your house and came smashing through your door?
The Ryan Frederick case doesn't quite fit the scenario because the Chesapeake PD smashed into the house stated on the warrant, but if the Cory Maye case is any indicator, it doesn't look good. It's definitely not fair for the homeowner to have to make the choice between either protecting his or her family from what could be a predator in a police uniform or going to prison because the law doesn't allow a cop to be killed regardless if they made a mistake.