Yes, just replace system with the desired username in the script.
Sorry, I skimmed the code, there is no system to replace, so it must be done another way.
You’ll probably want to use a session manager like screen or tmux so your script can run in the background.
I assume you’ll also want to be able stop the script when desired and restart it later from the user it stopped at.
Since I’m not a programmer (I mean, besides printing hello world…), I’ll let others give advice on how to set up this feature properly, as well as safely managing the sending to millions of users 