Is there a reason you need to use the OpenWRT snapshot? It will be less stable than the release version the GL firmware is based on. Beryl already runs OpenWRT 19.x.
If you don’t want to use the GL UI, then you can flash the stable version of OpenWRT, you do it via uBoot to flash and also to go back to the GL UI.
But yes there is no release version of it yet. If you do flash the snapshot, beware it won’t be as tested as the GL firmware. The OpenWRT guys usually just add a file and run batch compilation without much deep testing.