Yes, of course! Before the trip's start date, you can always request to add or remove dates from the trip, subject to your Host's availability and agreement. This can be requested within your Trip Details page.
However, once the trip starts, the booking charges are locked in. The Outdoorsy Support team can process refunds for unused days of the protection package once the trip starts. Any other refunds of the existing booking charges must be authorized by the Host, so please contact them directly to discuss.