Well, that's what 7.3.4 in the spec is about. The ACME server might or might not be willing to accept new orders without making the client agree to the new agreement.
In reality, neither Certbot nor Boulder implement this behavior, so even if new T&Cs come out, your signing requests will not require accepting the new agreement.
I'm not sure what the plan for the future is. You could tack on --agree-tos to all of your commands in anticipation of future changes in behavior, but it doesn't make any sense today.
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I remember during last year's agreement updates, acmetool was one of the clients that refused to renew certificates because of the agreement change. However, there is this statement to consider: