>>1440
if you have compression on your kick before the EQ, then yes, reducing high frequencies reduces headroom, and your compression will adjust accordingly.
Mixing is not about just arbitrarily cutting out huge chunks. don't adjust more than +/- 6db on EQ except if it's part of the sound design in the first place. unless it's got something really horrible that needs notched out.
As for specifically the kick, a kick is a sweep from high to low, very fast. this is where it gets that thump, and with a higher starting point and a different rate, you get more of a click. Otherwise, all you have is a sub. so when you EQ Out your high end, you're altering the phase a tiny bit and distorting it, and you're creating a sub, in the most counter-intuitive way possible.