call/alert me when I receive an SMS from a VIP I'm an Australian, and I've signed up to receive SMS alerts at different (unscheduled) times during the USA's day time, which is Australia's night time.

I want to ensure I am alerted when I receive an SMS from them.

Is there a way I can change the sound when I receive an SMS from that VIP?

Ideally, I'd like an alarm that wouldn't stop until I attend to it.

Help appreciated.
Found a partial answer, which will allow you to select a Sound. 

But not sure if I can set this sound to repeat until I turn it off.


Tap the Conversation you wish to set a custom notification for.
Tap the three-dot menu icon in the top right corner of the screen.
Tap Details.
Tap Notifications.
Tap Sound.
Tap your desired tone.
Tap the back arrow, or OK or Save if those options appear with your ringtone picking menu.


Source.