Hello Jessie,
You may also wish to log an Idea for this. It comes up every now and then.
It was documented in that a customisation was possible. It just wasn't defined in detail.
"I managed to achieve this by creating a customized pre-save trigger, spell customization also works fine here."
akhan.1 - I see that you're still posting on Service Desk Manager. Would you be willing to share some more details on how you achieved this? Or general suggestions?
Thanks, Kyle_R.