Locked templates made very difficult to change to discovery in global default templates, user needs to unlock 2+2+2 (PXELinux, Grub, Grub2 template + discovery snippet) and make necessary changes just to change the default menu entry. This can be done via global setting.

Edit: After some discussion, it will be required to have explicit list of global settings which can be accessed by the helper. Also templates can be also modified to use host/hostgroup parameter when present to override the default behavior.