Save Permanent Record of Dropdown Choice

I am creating a checkin system and appointment system for a food pantry.

1) Client (basic information, name, address, etc) 
2) Future Appointments (available appointment dates in the future for clients) 

When our staff assign a future appointment date, it's done by a multiple choice box. That works.  However, we'd like to retain a permanent record for each person's assigned future date, as the dropdown will change next month when we assign the next visit.  

Anyone have any creative ideas on how I can have an action link or other method that would save the status of the CURRENT dropdown for permanent records?  



I am uncertain of your Object and field structure so there are several possibilities but I am guessing that the Future Appointments Object is merely a list of appointments that is selected with a connected dropdown field in the User base? If so create a 3rd Object called Appointments and connect that Object to both the User and the Future Appointment objects and insert a new record to that Object at the time you set up your Client Appointments by using a Record Rule to insert a new record in a connected object.