When the Customizable property is true, the user can remove buttons from the toolbar by dragging them off the toolbar when the Shift key is pressed or using the toolbar customize dialog. OnCustomizeCanDelete occurs when the user tries to delete a button in one of these ways, and allows the application to reject the deletion. If the OnCustomizeCanDelete event handler sets its Allow parameter to false, the tool button returns to the position it occupied before the user tried to delete it. 

Customizable 

OnCustomizeAdded 

OnCustomizeCanInsert 

OnCustomized 

OnCustomizeDelete 

OnCustomizeNewButton 

OnCustomizeReset 

OnCustomizing