You can manage all default scripts for sure. Especially scripts, that you ask for, are located under the following item: /sitecore/system/Modules/PowerShell/Script Library/SPE/Reporting/Content Reports/Reports/Content Audit
Choose script that you want to change, click on Elevate session button, enter a user password and you will see a source of script in the Script body field.
UPD: @Michael West added an important comment. You should think twice if you want to change the default script as you will erase your changes with your next SPE module upgrade.