That particular dish has had several threads full of discussion just in the last year.
With 123° & 125° so close, I would be concerned they'd interfere on that dish.
MikeInBaja seems to have gotten 123° to work on it, but claimed it was a pain to aim.
He's only started a couple of threads in the FTA section, so it should be easy to find his exploits (has a silly name on the thread, though).
The lnear LNB needs to be kept at the focal point of the dish for best performance.
So, you could locate a 2nd LNB either to the east side (for a more westward satellite), or to the west side (for a more easterly satellite).
I wouldn't expect great performance of an offset LNB unless:
- it was aimed at a high-powered circular satellite (NASA on 119°, for instance)
- it was aimed at an easy to receive DSS satellite (Whitesprings on 129°, for instance).
The forum is all about experimenting.
So, while the above are conservative guidelines, feel free to color outside the lines.