Peggy, we were also changed to the St Emilion excursion on 22nd PM (although the Regent reps keep insisting it's on the PM of the 23rd), but it conflicted with a Bordeaux vineyards excursion we have at the same time.
Right now on 8/24 we are booked also on Biarritz/Basque coast on AM and San Sebastián on PM. I'm going to investigate options to do SS on our own and will let you know. I know there are direct buses, and train (with one transfer) but I'm not sure if the times will be convenient. I'm also going to look into the cost of a driver (that might be pricey).