Only on official roms the updater performs device reset when changing beta and stable
While on xiaomi.eu one can usually dirty flash official recovery roms dated same or newer with minimal probability for misbehaviour. For sure nothing will be wiped if you do not wipe it in twrp
Yes, you can usually "dirty" flash same or newer global beta over .eu with updater or in twrp. Do take backups in case anything goes wrong. It will replace twrp with stock recovery, can be reflashed if you need it
Global was also based on China. Did they separate the versions development? If I recall it properly this is the very first time any MIUI has released global beta before China
Stable to beta/weekly no wipes required, usual "dirty" flash
Beta to stable-data wipe required as you are flashing an older over newer build unless you have older beta and latest stable
This weekly for the very first time completely messed up my Mi4. After reboot seemed fine but several seconds later random FC`s started which caused system crash and recurrent reboots. Restored 8.4.12 backup(which wipes data and system) but still faced same reboots, flash again 8.4.12 did not...