All the do-gooders will tell you you can't and it's not allowed.
Would that be all the people who think it's right to abide by the rules set out my the business they ar dealing with rather than set their own?
Fact of the matter is I don't think the cruise line ever had any objections to people bringing liquor onboard to consume in the privacy of their cabins.
They instituted more stringent rules against liquor when they found so many people bringing liquor onboard, mixing their own drinks and taking them out into the public areas of the ship.
The old rules sort of proved the addage... give em an inch, they'll......