Actually, your selected method for controlling Wired WAN is quite good as there is no direct SMS utility to disable Wired WAN connection.
There is a way to disable Wired WAN with UCI commands, but for them to be executed it will probably take more time than just switching profiles with SMS.
uci set network.wan2.disabled='1'
uci set network.wan2.enabled='0'
uci commit network
These commands would need to be executed to disable Wired WAN and they must be sent as separate SMS, so I think it's easier for you to stay at profile switching.