No, any changes made to the group trip itinerary after sub-trips are created will not reflect on the sub-trips.
New sub-trips created will use the existing group itinerary settings at the time of their creation.
FAQ If I edit a Group Trip itinerary after sub trips are created will those changes propagate to the sub trips?
Editing group trips after sub trips are created
Written by Jade Pathe
 Updated over 11 months ago