Once had a user manually change their ticket to Priority 1, which we used to indicate dozens of people/everyone down, because their M key only worked half the time they pressed it.
I think that's because many ticket systems implement the ITIL priority matrix??, or something. I've been away from helpdesk for a number of years now and only kind of rember a matrix I probably only kind of correctly described.
Our system let users pick only some of the matrix values, they couldn't declare a high priority, high impact, high urgency, ticket on their own. Like you, we handled setting the "true" value once the ticket was moved past level 1/evaluated by someone in IT.