Modify only a copy of an R/3 standard device type, not the original version. Otherwise, your changes may be overwritten by the R/3 standard when you upgrade your system.
To copy a device type, do the following:
Enter a name of your choosing that begins with a Y or a Z.
Mark this option to have device format actions included by reference from the original device type. Do this when you plan only limited changes or extensions to an existing device type. Advantage: the device format actions remain up-to-date with changes made in the R/3 standard device type.
You want to customize the cover page but plan to leave other actions as they are. You can completely replace the cover page action(s). Other actions reference the actions in the R/3 standard. Any updates by SAP are automatically reflected in the referenced actions.