You are potentially able to move duty free periods (Days Off). You can do it two ways. 1. Trade with another pilot, 2. Call Crew Scheduling a few days prior to that reserve block and ask to move one or more of your days off to another day. I have asked CS to move a day off 5 times in the past year. Each time they have moved it to the day I wanted, except for one (It would have made me 117 illegal). The key is to move it within a few days so they see they have coverage. I usually do it to extend a larger block of days off. CS can say no.