What's the easiest way to make a perk triggers On Kill?

[hydralisk2]

There are some entry points that trigger on vats kill, but they only work for specific perk's purpose such as grim reaper sprint.

Is there an easy way to make a perk triggers on kill?

For example, if player kill a target with bare hands, then player get certain buff.

And is there an easy way to add a cooldown to a perk/spell?

 

Thanks very much.