Changing Built-in List Field Types

Hi,

I'm looking at the task list template and adding the Categories built-in field which maps to the Categories field in Outlook. Instead of a freeform textbox I was thinking about a drop-down or multi-select list to help enforce consistency of input. From the list settings side there doesn't appear to be a way to edit this. If I export the list template, change it in the definition, and then re-import it, is this supported and will it map back to Outlook using the same field

Cheers,
Colin