Lighter bullet, same charge?

Hope this is in the right section.

I'm pretty certain going with a lighter bullet will not require me to reduce my charge, but wanted to make sure there is nothing I am over looking.

I was pushing my own cast 135gr TC'S with 5.0gr of BE86. I am out of bullets and bought some "Black Bullets" they are 135gr cast (acording to the ad, my scale has em around 117.5). My same charge should be fine, right? I didn't see 135gr cast listed on Alliant's guide but noticed they reduce charge as weight goes up (the way I have always understood it). So going down 20gr, in bullet weight, shouldn't do anything (leaving the charge the same) except up the velocity a wee bit, right?

Correct. The only time it makes much difference is when you go from cast to jacketed or the other direction.
When you have a boolit that doesn't have data listed for that specific weight, one of the best suggestions is to use data for the next heavier boolit. This gives you a place to start.
If you have a chrono and have tested your old boolits, test the new ones and see what changes occur if any.