access to duty free which has been surrended midway during a cruisea

We are doing a middle east cruise next year and while we are in Muscat we will be visiting some friends who live there.

As Booze is resticted to expats living in Oman we would like to buy Duty free and take it to them when we visit.

However we expect that the duty free will be conficated on boarding. Has anyone any experience of getting the duty free back mid cruise to take it off shore.

Thanks

Someone has told me there is a duty free shop when you get off the ship.

Are you allowed to buy when you depart the ship or only on boarding?