The headpin UI allows the CDN repository url to be changed on the 'import manifest' page. This value, however, is not propagated to the thumbslug.conf file in any way. This means that the default value, https://cdn.redhat.com will always be used. Solution would be to open API to thumbslug to adjust this value and persist it to the thumbslug.conf file, or to have headpin update it directly.
On a further note, this CDN repo value is global to the entire install, it can never be adjustable on a per organization basis. It should therefore not be editable in the UI and only set at katello-configure time.
After some discussion the following was suggested: + thumbslug.conf will hold the default cdn url (as it does currently) + Each product in candlepin will be updated to allow having it's own cdn url. This is the broadest possible mechanism that will support third-party tools using the candlepin api (such as katello). + Additional parameter to the 'import manifest' api call to specify the cdn url to use (which would be applied to all products as a convenience)
Next SAM release does not use thumbslug