Hot To Activate a New Widget Class

Trying to get my head around creating/modifying widgets.  I want to take control of the widget that displays the subject line of an email in the History subpanel display.

I've copied ForHistory.php for the Emails module to  custom/modules/Emails/metadata/metadata/subpanel/ForHistory.php

Within that file,

For the vname LBL_LIST_SUBJECT in the array I've renamed

'widget_class' => 'SubPanelDetailViewLink'

to

'widget_class' => 'SubPanelDetailViewEmailLink'

I copied SugarWidgetsSubPanelDetailViewLink.php in custom/includ/generic/SugarWidgets to SugarSubpanelDetailViewEmailLink.php file and made modifications.

The modifications aren't showing even after a repair and rebuild.  I can modify the SugarWidgetsSubPanelDetailViewLink.php and I can see the changes right away.

What am I missing?