Adding a field to the address in Contact entity

Hello Team,

We are using Dynamic crm 2015.

in the outofbox address field comes like a set which includes the street1,street 2, street 3, city, state and zip.

In the state field I would like to show this as an option set but  we cannot change the datatype for the outof box state field.

If I add a new field I will be loosing the outofbox feature to show the address a composite key ( single box)

Any help or guidance in achieving this is highly appreciated.

Thanks,

Jeevan