Name the fixed bookings explicitly
For a weekend plan, “Keep the Saturday train and the hotel. Suggest two Sunday activities within walking distance” is specific. If both suggestions need a car, reject them against the original constraint. Keep a copy of the confirmed arrangements separate from the draft itinerary. Include the train date, departure station and hotel reservation already confirmed. “Keep the trip the same” leaves the assistant to guess which details you consider settled.
Set the space for alternatives
Ask for two Sunday activities within walking distance, with an indoor option if practical. Require uncertain facts such as opening hours to be labeled and verified with the venue before booking. If every proposed activity violates a fixed constraint, report that result instead of relaxing the constraint silently.
Keep suggestions away from confirmed records
Draft options in a separate note until someone accepts one. Compare the chosen activity against the existing travel times and any booking cutoff. A useful suggestion can still be a poor replacement for an existing commitment, so update the main itinerary only after the household decides. If the venue closes on Sunday, replace the suggested activity. The confirmed train remains part of the plan.