Moving a ticket from one desk to another

HI,

I am trying to find a way to move tickets from one desk to another. For example, a ticket comes in via email to our Incident desk. However, what the user is requesting is to purchase something from us. I have a sales desk set up, and I'd like to move it out of the incident desk and into the sales desk. 

When manually creating a ticket, I can see a drop down list where I can choose my desk. However, once a ticket is created, that field becomes greyed-out and can't be changed manually. I thought I could create a procedure that would check the Category field, and if it had been changed to "Sales", it would move it to the Sales desk. However, the "Service Desk" ticket property does not seem to be available except in the Ticket Request Mapping section.... 

Is there a way to do what I'm trying to do?

Thanks!

--arthur