This news was being cooked by the MIUI forums, but it was not something that was 100 per cent confirmed. Now, from the same forum, it has been confirmed that the Xiaomi Redmi Note 5 and its Pro version have a system that prevents it from returning to MIUI 10. You can not go back to an earlier version of MIUI, even if it’s global or beta.
Moreover, the consequences of trying it are fatal. According to the post of the forum, if you try to flash a ROM before MIUI 10 to downgrade the device, the phone will be unusable or bricked. A fatal consequence.
The administrator who has given the news recommends is logical: if you are in MIUI 10 do not even think about flashing another ROM. If you are not in MIUI 10, do not update until the stable version comes out via OTA. The reasons given to include this system are in pursuit of the safety and stability of the device.
We do not know why Xiaomi has done this. These devices are called to be the new super sales of the firm, and part of the community will want to try MIUI 10. The fact is that it is not a version fully suitable for daily use, being a beta. But we’ll have to wait for how Xiaomi manages this tricky issue.