I’d suggest that you not do this over an existing connection using the impacted interface, without considering that it will “upset” the ARP tables and may result in a significant delay in reestablishing the connection, even longer if a TLS handshake needs to occur.

One way to accomplish this would be to use a script (that could be, for example, securely executed over ssh with a command-bound key pair) to either edit /etc/config/network directly, or use UCI to set the “macaddr” option of the interface in question, then call /etc/init.d/network reload. ubus could also be used to make the change.