When we were in our last cruise, uncertain of changed itinerary, I asked at the excursion desk in the Galleria-although I guess YC concierge may do this for you. They seem well informed because they have to plan alternative excursions etc.
Maybe MSC are hoping the industrial action will cease and they can keep to their original plans?
As you said, it would be easier if they just skipped Le Harve for a while and made firm plans. This would be hard for people planning to board in France, getting coached all the way to Amsterdam!