I dont think the carriers should be allowed to have a setting to completely disable amber alerts.
What I do think is like on my phone after first initial alert you can dismiss the alert. And when phone goes to sleep as you wake it up the text massage appears of the alert and you minimise it with a button. The only disable for an amber alert should be a toggle to recieve text and sound message or vibrate and text.
As for working in an environment that doesn't allow personal cell phones well you shouldn't have it with your or it should be turned off. The reason for the repeated alerts are for people that may have there phone off or are away from the phone. You get your breaktime on your phone and get the message .
Just my 2 cents maybe be better ideas out there keep them coming.