Often when I kill enemy NPC's "too quickly", they say "Be careful!" or "What's the hurry?!" etc. I find this a bit annoying and immersion breaking, especially with enemies that are supposed to be bad guys. As there doesn't seem to be any mod dealing with it I thought I'd take a look myself, but I have no idea where to start as I've never messed with dialogues. Any pointers would be appreciated.

If you're talking about when someone is not an enemy, and then becomes one through a dialog or trigger, the only way I know to speed that up is through calling them to "EvaluatePackage". It just takes the game a second or two to catch up with itself and all the scripting and what not to thread. It would be a pretty monumental task to figure out every instance in the game this could be an issue and scripting those calls in. My suggestion is to just be a little more patient!