There may be a time when leveling a character that the characters priority switches from adventuring to spending more time in town with RP. In this case, if you chose the Professional Contract, it would be beneficial to you to swap to a Freelancer Contract.
To prevent cheesing this, some stipulations must be added. An upfront cost of some amount of gold is the first. Adding a cool down period between when you swap is another. Maybe everytime you do this it costs more (10,000 > 20,000 > 40,000 > 80,000 etc.) Or maybe it's a one time swap with an upfront cost.