AirmanDeRuiter

This is a mix of different agency's, but its what I go by
-How/when a cop would and would not use his lights/siren
Priority calls, such as crimes in progress or when time is a factor. Locally, our officers can choose when to respond "Code 3"
-How/when cops use unmarked or partially marked vehicles
There's not really a statute, but our traffic section uses unmarked, and obviously gang enforcement so they can stay undetected
-When a cop would use deadly force
When the officer feels that without using lethal force, himself or others could be severely injured or killed. This is a sole judgement call on the part of the cop
-When/if a cop would ever use his vehicle as a weapon
Same answer as deadly force. If its going to stop the suspect from maiming or killing, its better to use it and answer for it in court
-When would a cop call off a chase
This is a touchy subject. If the suspect was being stopped for a simple infraction "summary in canada, or misdemeanor in America" and he runs at a high rate and dangerously, air units would be called and units would break pursuit. If he is wanted for severe infraction "Indictable in Canada, or Felony in America", the chase would continue as letting that suspect go could endanger more lives than the pursuit. In game, make a judgement call
-What are the different ways a cop would respond to a call i.e. obeying regular traffic laws/slightly modified traffic laws/going full on lights and sirens full "safe" speed
These are code calls.
Code 1 or non priority response, is to respond cold, all traffic laws and no lights or sirens.
Code 2 or expedited. This is a little different depending on agency, but usually normal speed and clearing intersections with lights
Code 3 or priority, is to respond hot. Fastest speed that is safe, lights and sirens.
Hope this helped

1- See point 6.
2- Unmarked cars can be used in any time, it's used for Patrols like it was a normal cruiser.
3- A cop would use deadly force for when the suspect maybe holds a weapons (either real or fake) they first react is to open fire to defend themselves. Sometimes suspect survives and other times it doesnt.
4- When, a cop would use their car as a very very last resource to stop the suspect mostly when he's in a car using PIT maneuver.
5- _ _ _ _ _
6- That depends of the Code the dispatch says. Code 1= normal prior (Obeys all traffic laws | no lights no sirens). Code 2= medium prior (Slightly traffic laws obey | lights on | IIRC they use sirens on intersections only). Code 3= high prior (Full lights and sirens).

Hope this helps you, I may be wrong with some points.

In response to some of those questions you should expect slight variation with answers, different law enforcement agencies have different ways of dealing with these sort of questions. I am going to answer these questions in the way that my own force deal with them.

-How/when a cop would and would not use his lights/sirens
We'd use them in an 'emergency' usually that would be a call-out from dispatch to any kind of 999 call. However, when we are responding to transport detainees then we'd go without lights, just as we'd run no lights helping a officer that hasn't stated the assistance is urgent.

-How/when cops use unmarked or partially marked vehichles
For us that always depends on what operation we're taking part in, usually pro-active force officers use unmarked low-range cars to catch criminals in the act. We do however sometimes use um's for maximum stealth!

-When a cop would use deadly force
When a civilian has been wounded/killed, when an officer is reported as down, or when an officer's life is in danger

-When/if a cop would every use his vehicle as a weapon
Don't understand the question- I assume you mean hitting people with our cars? NEVER

-When would a cop call off a chase
When the suspect becomes a 'severe danger on the road by driving extremely recklessly with no regard to human life'

-What are the different ways a cop would respond to a call i.e. obeying regular traffic laws/slightly modified traffic laws/going full on lights and sirens full "safe" speed
Whenever we activate our lights and sirens we are responsible for ANY damage we cause, from a snapped wing-mirror to killing someone. Therefore to 'cat.4' calls we respond without lights or sirens- usually we only respond without lights to fellow officers because we know they have a better chance of suppressing an assailant than a random member of public.

Hope this helps you a bit, however don't feel to do all this in game... even I go on rampages in it from time to time!