If you are threatened with force(Lethal OR non lethal) they have the same "strength" if someone says xyz hands up or die you can kill them. If someone says xyz stop or you shall be tazed, you can also kill them, that is my understanding of the rule as lethal & non lethal initiation count as the same thing(Please correct me if I am wrong)
No you cant shoot imidiately back if a cop says hands up or you gonna be tazed. After he says that you need to give rp back or counter initiate what most people do and if you think that you have given enough rp and the next time the cop says if you not gonna put your hands up im gonna taze u then u just spray him down.