Hi Menox,
I have found that when the kites are new, the back line adjusters are better to be pulled in all the way to give more feel to the steering. After a few weeks of use, as the front lines stretch to their normal length (an inch or two) the back lines will even up and then the factory setting is about right on. As PR said, by having them pulled all the way in, after the lines have "bedded in", it may start to back stall a little.
I generally adjust the back lines to suit the way the kite flies on the day. Most of our kites have all bedded in so it is pretty easy to just set the back lines to the factory mark. Easing out the lines can give you a bit more range in the top end but I prefer to use the kite trim for that.
The 5th line knot at the end of the line is for normal power, the knot closest to the kite is to increase the steering speed and also depower the kite just a little to give it even more range.
You cannot re3move the red ball to increase the depower of the kite. If it doesn't depower enough as standard you really shouldn't be out. I have held Edges in really crazy wind speeds with only an inch or two of trim. The trimmer has a huge effect on the kite and only a few inches are generally needed to depower the kite sufficiently in the strongest of winds.
Although they are very stable in extremely overpowered conditions, I don't recommend you continue to fly them massively overpowered as they still have a wind range which should be observed. You should always ride within the kites wind range and that goes for all kites, especially as a beginner.
The mod to the Light II's is basically moving the point of leverage closer to the wing tip, thus giving you more leverage. It wont really increase turning speed but does make it easier to turn and slightly lighter on the bar. I tried this mod on the 07 Sports when we first got one and it made little difference.
I hope this helps.
Good winds,