ServiceNow modify out of the box object or work on a copy?

see

https://developer.servicenow.com/dev.do#!/guides/rome/now-platform/pro-dev-guide/pd-build-logic#modifying-default-behavior  

In the past, one of the strategies used was to copy the artifact to update and to deactivate the original. The copy/deactivate approach is no longer recommended due to the following issues:

• Developers cannot tell if a deactivated artifact was upgraded without research.

• Two files, the original and the copy, need to be maintained. Maintenance doubles each time a customization is made.

• With each release, the customized record becomes older.

  • Customers do not receive the enhancements included in a new release.
  • A new release may rely on the original record being updated.
  • Developers may make more changes to compensate for the original record being inactive.

A script where only the Active flag is changed will be updated, but the script does not appear on the skipped list. With the copy and deactivate strategy, a developer has less visibility into customizations and cannot easily assess or revert to the baseline version.

Rather than copying and deactivating the original artifact, edit the artifact directly. The ServiceNow Upgrade Engine will add the latest version to the version history and report that the artifact was skipped. Developers can see a new version is available with the upgrade.