I didn't know that date change restrictions applied to partner redemption awards. We changed dates on a BA miles redemption after the first flight in 2009 on LA (from IPC to SCL) with no trouble. I think either that things have changed since then, or that you are perhaps referring to redemptions on BA metal (where BA's rules tend to be much stricter than on partner airlines). Can you please provide a link to T&Cs that mention this prohibition?

One well-known problem with BAEC partner awards with stopovers is that they must be made over the phone, and therefore attract significant booking and service fees (that could be avoided on simpler itineraries booked online). Changes also must be made over the phone, to the same BAEC office that made the original reservation, so one must keep track of the hours and telephone number of the BAEC office where the reservations were originally made. The relevant fee schedule is here:
https://www.britishairways.com/trave...club/_gf/en_us