The “Add Repository” feature has an option, currently labelled “Import existing repository ?”.
That label is misleading; “import” implies a one-time operation that will not make a persistent setting on the new repository.
Instead the operation is to set a remote repository for the new repository. A better label should be chosen to reflect that this is not a one-time operation.
Possible improvements might be: “Inherit from an existing repository”, or “Set an upstream repository”.