is there any way to update a text field on a form automatically as the status of the Work flow BP ch

for example,

We have a BP for Invoices.

Once the invoice is in entered the record status is "Pending", and Payment Status (Text field on the form) should say "Not Processed" (Automatically) 

and

when the Invoice BP Status changes to "Approved" through the work flow tasks,  Payment Status should change to "In Process"

Any Idea on how this could be done?