Note that it is not necessary to book travel for May already now, unless you are doing it for the discounts…
Trains are mass transit. Tickets are for a route, not a train. A Strasbourg - Luzern ticket allows you to travel from Strasbourg to Luzern on the trains that are available to make that trip. If those happen to be different trains than the one offered when you bought your ticket then you just take those other trains.
So do not worry. There will be transportation. And the schedule you see now is already the modified schedule. The warning is there for people who might wonder why their train is not leaving at the usual time or is taking a bit longer than expectex…