Hi John,
I believe you may be able to accomplish this by using an event and action macro. The event would detect an update to the field that you are changing, and then the action macro can set the category to something specific (it would have to be static though - meaning a single value can be used all the time - there is no functionality to do dependencies or anything). I have not attempted to do something like this myself as its typically not within the scope of support to configure this type of thing for a customer, so I cant say for sure that its 100% possible, BUT, given the functionality of the application, in theory, it should be.
Hope this helps,
Thanks,
Jon I.