Re: crossing line and load in a breaker panel
You won?t find it in the NEC. It is a matter of satisfying the installation and usage requirements of the manufacturer. If the manufacturer says you can?t, then the NEC will tell you that you must follow that instruction ? see article 110.3(B). Otherwise, it?s not illegal.
I can think of no physics-based reason for not allowing it. My only concern is whether there would be enough physical space for routing and connecting wires.
Do you have the option of buying a different panel (i.e., with lugs on the bottom)?