In CodeWarrior Development studio the on-chip reference is automatically trimmed and programmed into Flash each time a debug session is initiated and code downloaded into the target. To change the default trim value select "Debug Configurations..." from the drop down menu next to the debug icon in the toolbar:

In the resulting dialog, click on the "Edit..." button in the Target settings area:

In the next dialog box, click on the "Advanced Programming Options" button:

In the final dialog box, use the trim options at the bottom to set a custom trim value:

Hope this helps.
Regards,
Gordon