The Custom Installation Script tab enables you to insert Windows batch file commands directly into the installation script. The commands can be executed before or after the update is installed. If any files are required in order to execute your custom commands, they can be added to the update package.
For example, you could use this feature if you want to stop and restart services, remove conflicting software, or perform custom logging.
If you want to apply custom installation commands to all updates in a supersedence chain rather than to just an individual update, see What is an Update Template.