Comment 7 for bug 1879350

Ok, so actually this is much easier. After talking with mvo it seems that grade dangerous models can have their channels freely overridden, which means no new model assertions need to be created. What I did is I prepared an upload for livecd-rootfs which adds the support for dangerous-<CHANNEL> channel. Once such a channel is given, we will use the dangerous model (which defaults to edge) and then override it with the channel name that's supplied after the -. I did a test build with this change and it seemed to work:

https://launchpad.net/~ubuntu-cdimage/+livefs/ubuntu/focal/ubuntu-core/+build/218342

Pushed it to the ubuntu/focal branch and uploaded to snappy-dev/image. I also switched cdimage to build the new images.