What in a Supernet do you want to edit? You can also edit the Supernet name as well and if you have custom attributes at the Supernet level, you can edit those.
VLAN and Location are not fields at the Supernet level, but at the Subnet level they are editable.
Could you provide a little more info?
I deliberately put a supernet in wrong just to see what I could do after the fact. I wanted to change the beginning address of the /23 and couldn't. The only fields I can edit are name, CIDR and description.