Add a new field to a report?

I'm just getting started with the out-of-the-box reports that are included in Desktop 10.0. I foresee several revisions off this report before we settle on the final look, which may include adding new fields. I created a report using the wizard and got the default report layout. But I didn't see a way to add a new field to the details section of the existing report. What happens if we need to modify the schema of the table that drives the report? Can we add a new field to an existing report layout without having to start the report design/layout process over? This will be one complex report layout and restarting every time we make a schema change will be a major head ache

Thanks