[weirdinin]

A simple question : is it possible to migrate from/to Windows MVC build from/to Kodi Beta 3 and keep userdata ? Is it necessary to uninstall old version before ?
Thank you.

I would strongly advice you to backup your userdata folder when migrating from/to another test build even if userdata should be intact! At least backup your database folder or export your library to xml files (I do both). Once when I tried various non mainline Kodi versions, database was messed up and I spent entire weekend to fix it. I export library to xml files and take a copy of the entire userfolder every time before upgrading/downgrading Kodi.