My advice would be to work out your IBU's if you don't already. Theres some equations on this site
and plenty others. It might put you off at first but its pretty easy. Say your last beer was 60 IBU's and you found that too bitter; just reduce the bittering hops by a half (or whatever) and you'll have 30 IBU's - then you'll know what 30 tastes like. Theres also plenty of applications
which will to the maths for you. You could haphazardly throw them in late but you won't have much of a reference point for next time. Plus you might be overwhelmed with aroma.
But yeah, like the guy above said, just ditch the kits and make your own up (using a recipe as a starting point). Theres tonnes of hops easily available to play about with - check out the hops preference poll on the recipe forum. The alpha acid rating gives you an idea of how strong they are.