When trying to update the interface used for a WAN interface we are finding the option greyed out to change the interface on a WAN even when selecting "Override Template Settings" (ie: WAN1). The interface can be changed from the template, but not at a device level. We are trying to understand why this option is greyed out- it seems we should be able to override the interface when selecting the override template option.

For example- I was trying to change this interface from ge-0/0/0 to ge0/0/3 and the option is greyed out.

When the interface "label"/"name" is hard-coded at the template level, it cannot be changed; only its contents. If it needs to be "editable" and dynamic, then using site variables for the interface labels/names would work, you will be editable at the site variable level.