Hello there in Asheville :)
First off are you saying that you have made a decision to switch agents, but plan on continuing the listing agreement through the end term shown in the agreement? And you are worried about getting a contract between now, and when the contract ends, such that you would be continuing to work with that broker past the contract end date? Sorry I'm just trying to clarify your intentions.
My suggestion would be to contact the Broker and discuss your unhappiness with the agent.
If you don't want to work with the agent, the broker can assign a new agent to work with you based on your needs. And you can continue with that Brokerage Firm. As Will Nesbitt explained, the contract is with the Brokerage Firm, not with the agent.
If you truly don't like the brokerage then you can tell the Broker that you want to terminate the agreement. Send them written notice and have them acknowledge it.
These rules vary state to state. But talk to the Broker first.
Will's advise, below is excellent as well. He is a Broker.
Hope this helps.
Delaine Campbell, MBA, REALTOR(R)