Swap the order, not the whole trip
Look at which activities genuinely need dry weather. Move an outdoor walk to another part of your stay if possible and use the wet period for something indoors. Avoid rebuilding the entire itinerary around a single forecast update. A flexible outline is easier to adjust than a full timetable.
Pick one indoor place to enjoy properly
Choose somewhere you actually want to spend time, whether that is a museum, a cinema or a bookshop. Check its current opening and entry arrangements before setting off. Resist the urge to string together several distant stops just to keep busy; travelling between them can take over the afternoon.
Make lunch part of the day
Leave time for a proper meal instead of treating food as a quick pause between sights. Bring a book, sort through your photographs or talk about what you have enjoyed so far. You do not need a famous restaurant or a tightly planned reservation to make a slower lunch feel like part of the holiday.
Keep the evening simple
After a damp day, an easy return to your accommodation can be welcome. Dry out your things and decide whether you still want to go out. It is fine to choose a nearby dinner and an early night. Tomorrow does not need to carry every activity you moved from today.