Designs are used for such cases if working with simple pages. I've tried adding /etc/design for Facebook Experience Fragment. I've added cq:designPath to the template. But I can't configure the right structure for this design.
Right now my design looks like this:
/etc/design/experience-fragment:
_jcr:content (with sling:resourceType set to wcm/core/components/designer)
__experience-fragment-template-facebook
___initial
____root (with components property specified).
No new components are allowed to be added to my experience fragments though. I would appreciate your help.