second set of knots on brake leader on flexi handles. what does it do? other than putting more brake on the kite.

Probably gives the KS-P-A-M-L-I-N-K-s somewhere good to hold on to without being tied to the flying lines. Just a guess.

could they be a way to adjust the breaks?

Yes it is to adjust the brakes.
That's where I hook my brake lines up. During the first flight I saw how saggy the lines were, so I moved them to the second knot. Plus like Pablo said now the kite killers are not rubbing on the brake lines.

I tie kite killer between first and second knots on break leader.

Some kites prefer to run with a lot of brake the Samurai are like that. Some of the race kites like this action to, its like flying along add a little brake and it speeds up, release brakes again and wham another gear...

Just another quick point, do not put your kite killers on the down side of you handle or bar.
When you release the handle will flap around with all that power you were trying to get away from.
Not a good scenario, I'm guessing.
Always use your safety gear in the way it was intended to be used.
Cheers
Winds picking up here, could be a good day a little cold -22 but sunny:saint: