if you try to change the remoteurl entry you get something like this:
"error saving project: Repository openSUSE.org/snapshot cannot be deleted because following repos link against it: ..."

1. it should validate that the repositories are really not existing on the new url. it seems it just assumes "changed url, must fail"

2. in most cases where it required removal of a repository, we only had to remove one repos and not all of them.