Yes, an Out-of-the-Box report can be edited. It is recommended to make a copy of the report and edit the copy to ensure the original integrity of the Out-of-the-Box report. For additional protection of the Out-of-the-Box reports, make a copy of the entire Legal Reports folder and add private level security to the originals. This way the originals will be hidden from users and cannot be altered.
Here's how to edit an out-of-the-box report from Legal Reports.