I am sorry that I can't reproduce the same issue as you, with the script you offered above, I just have the Unique key and the FullCode column created for the first time when I deploy the database project. In addition, what about other database objects?
Will they be deleted and recreated again as well? If so, please make sure you don't select the "Always re-create database" option in the Database.sqldeployment file.
And if the above workaround does not resolve your issue, I think maybe there are some other database objects in the database project cause you the Unique key and the column re-created. It is better if you can provide me the sample project which can reproduce
your issue. I would like to take a look at of it for you.