That’s weird. That problem existed in the 3.4 build bit should be fixed in the 4.0 build. I will experiment to see if I can reproduce it here
It should be possible. I quite often swap between Android versions on my test device without any problems. You will probably have to format your data partition, so back up your apps and data fore you change. As mentioned above, this build
I used that tool to migrate my ‘daily driver’ device from my custom L4M build, without any problems. And I have used it in the past to migrate apps and data to a ROM running an older Android version.
That would be great, but don’t hold your breath, for a number of reasons 
- Iodé (correctly IMHO) do not seem to be in any hurry to add new devices, and they do not have any defined pathway for having unofficial builds become “official”. (thouhg I am not aware of any other unofficial builds apart from this one and the build I made for PIxel 4a
- This device is not officially supported by LineageOS, and I don;t know how Iodé would feel about that
- Also, their policy is to only make and ship
userbuilds without rooted debugging, which means the ABRT tool wont work. As that tool is essential to my workflow, and as there is no other working way to backup / restore / migrate apps and data, I won’t be making any user builds
What might be possible is for them to agree to allow unofficial builds to be distributed OTA using their infrastructure. It’s not something I’ve raised with them, bit I could ask
I hope the build works out OK for you. I am enjoying using IodéOS