Please keep in mind that the related "Disable Modify and Disable Repair" options will be applied only for "Add or Remove Programs" applet in the Control Panel.
In order to achieve what you want you can go to "Dialogs" page, select "MaintenanceTypeDlg" dialog and for [Modify] and [Repair] buttons set their "Visible" and "Enabled" attributes, from "Properties" right pane, to "False".