The SOP in my company is that the PIC has to be the PF in LVO (RVR of 400m or less for take off, less than 550m for landing), therefore he has to taxi.
The second case (CM2 as legal commander) is undesired, but happens from time to time of course. In that case the PIC has to do all the usual PIC duties, the CM2 does all the stuff an FO does. In LVO it will the PIC taxiing and the CM2 assisting. However, the hierarchy gradient is wrong and there is an increased risk of CRM problems and therefore incidents, which is the reason why it is not a normal and desired crewing solution.