Ticket priority field

Has anyone ever set RT up so that a customer can set this priority field
when they submit a case ?

Also, I need to map SLA type priorities (1 - 4, 1 being the highest) to RT
priorities (arbitrary number increasing with priority)

Anyone done anything like this ? I have the nice chunk of perl to increase
priorities over time, but this is a little different.

If you haven’t done it, do you have any ideas on how to approach it ? I’m
not yet very familiar with the innards of RT. I’m running v2.0.15.