I can only speak for Florida but as for shooting the guy with something less then lethal (ie birdshot) from what is considerd a lethal weapon (a shotgun) may not be a good idea. If you do not think that deadly force is justified, you should not shoot. Thats why cops (in our area at least) can't do the infamous "Warning shot" because any discharge of a weapon is considered deadly force whether or not you actually intended to kill the guy. So, if you say, well, I just wanted to scare/wound him.....look for an indictment to follow shortly thereafter.
Now, if deadly force is justified, there is no limit on the manner in which it can be applied. Take for example the batons we are issued. We're taught not to strike certain areas that are likely to cause death or great bodily injury, the head being one of those. Now, consider that I'm in an up close confrontation hands on with a BG and I have my baton out. BG pulls a knife and the rules change. The head is now a viable target because I'm justified in deploying deadly force. Why did I use my baton instead of my sidearm? I had the baton in my hand and his head was available. Of course, if I can withdrawl and go to my handgun, thats my first choice.
Someone standing in front of my patrol car pointing a weapon at me and it puts me in fear for my life? Do I get out and engage or simply run him over? I choose to stay with the 2000 pound battering ram that provides at least a little cover. Either way, the guy is dead and my actions will be judged by the facts as they were available to me at the time of the incident.
"Why did we shoot him 96 times? We ran out of ammo." - Sheriff Grady Judd, Polk County Florida after the shooting of Angelo Freeland who had murded D/S Matt Williams and his K-9 partner Diogi. (Not necessarily a fan of his but he got it right that time so I'll give him due credit for guts)