In case you’ve wondered is it possible to have two separate working ROMs on a single device, my answer to you is yes! This is possible by using the DualBootPatcher which is currently working perfectly fine on Redmi 4X (santoni) phone.
Original source: XDA link
Find more information in the official XDA thread. Please note, that you’re doing everything at your own risk and we’re not responsible for any issues or bugs.
Below you can find download links for working DualBootPatcher. The mirror link is available from our high-speed servers.
Download link: Android_GUI-debug.apk