Not sure if best placed in this thread or another (mods feel free to move)

Myself + my partner are booked with priority rewards: YVR - SEA - IST (stop x 2 days) - BKK (dest) - SIN - JFK.
She has had something come up and needs to be in Munich instead of the IST stopover.

When PR's are used is it still possible to split the PNR, and then adjust her booking separately?
Trying to route her something like YVR - FRA - MUC - IST, then continuing the rest of the itinerary as booked. (- BKK - SIN - JFK).