Let me explain my question with the help of an example.
I have created a Generic Page Template with Slot's as Header, footer , Navigation, Cart, Search, created HomePage , ProductDetail Page, ProductLister Page based on Generic Page Template. By default Header, footer , Navigation, Cart, Search slot's were available on all the three pages. I have created a Banner Slot only for HomePage (I don't want this slot to be shared with the other two pages and hence not added it in Generic Page Template). Through HMC I was able to create and edit the content of the Banner and the changes were reflected on storefront.
I logged-in to CMSCockpit to see the HomePage and edit the content of Banner component. But I couldn't find the Banner slot. Rest all slots were visible. When I removed the Banner slot reference from page and moved to Generic Page Template, then I was able to see the Banner slot.
My question is can we edit the page level slot (slots which are not defined in page template) from CMSCockpit ? I hope, I was able to explain my question. If not feel free to reply back and I will try to explain it in different way.