The Data Type and Modeling Type properties of a column can only be set to the values permitted by JMP. JMP uses these values in the different analyses and graphics. So you will not be able to change the value to "Circular". However, there is the capability to create your own column property, and to use it to store such information. If you rt mouse click on the column header, and then select Column Properties, you will see a large number of property choices. One of the choices is "Other". There you can add any property you want.
I might be able to be more specific in my help, if you could provide more specifics on what your expectations would be for your "Circular Label"?