You can add new rules to an existing MAP-T domain while the MAP-T domain is instantiated and forwarding traffic. However, each rule must be in the shutdown state before any of its parameters are modified.
A MAP-T domain must be in the shutdown state to modify the dmr-prefix parameter. The remaining parameters (tcp-mss-adjust, mtu, ip-fragmentation) can be modified while the domain is active.
A MAP domain does not have to be in a shutdown state when rule modification is in progress.