I do not understand the issue unfortunately. What do you mean by "custom values"? Are you talking about using a different value type for the primary key (the ID column) instead of the regular integer one?
If you intent to import data, there is no limit on what kind of values you can import, as far as I know. If the primary key value type does not work for you, you can use any other attribute to store IDs of your imported data. With a unique index, any column can serve as key.