is there a cli command to set the destination IP and Port for multitx?

Hi and welcome to Digi Forum.

If you are referring to SarOS routers as I guess, the CLI commands are:

multitx 0 host0 “IP”
multitx 0 port0 “port”

For any further help, please review our support options on our website: https://www.digi.com/support

Regards

Anny
Digi Technical Support Team