As per my knowledge, only few selected modulation and coding schemes are used for MBMS transmission.
While doing the configuration for an MBSFN Area, this parameter is configured and broadcasted in SIB13.
One value out of (n2, n7, n13 and n19) is selected while doing configuration for an MBSFN Area.
All PMCH(s) will use the same modulation and coding scheme for transmitting MTCH data of all MBMS Services.