RE: dual aileron servos on sd-10
The L and the H are just low and high for the channel. On the normal channels, changing those is simply a matter of moving the stick. On the aux channels, it depends what control they're set to. Either a side slider, a knob, or one of the switches. You move it from high to low so you can set the various endpoints.
You may still get some binding if you're using digital servos and they're not matched exactly in speed and throw, but it won't be severe. Just minor as they transition together.