I am able to use fastboot method to flash stable global rom of miui 8 5.1 jellybean to developer global rom muiu 8 6.0.1 marshmallow 6.9.15 kenzo image fastboot version without wipe any data all setting retained.
You need to extract the tar file once downloaded like using winrar, then use winrar open up the one big file that is extracted from tar into a folder, then you will see some bat and image files there.
then download miflash utility, launch it. Put redmi note 3 pro into fast boot by pressing the vol up button first and hold it, then press power button to power up the phone, release the power button to see fast boot logo then release the vol up button. Plug in the usb cable connect from your phone to pc.
At the xiaomiflash program, click reflash button, you should see a device detected, click select button, browse the folder location which you extracted that you see some bat and images file then click ok. Select at the bottom right dropbox arrow flash_all_except_data.bat and click flash button at the top right. Wait for the device to boot may take 20 to 30 mins to completed flashing.
I have two sim card, one micro sim starhub and one nano sim singtel. Have tried both support 3G dual standby at same time. But if internet select starhub can go 4G, if internet select singtel only 3G so tomorrow I try other place at my office if singtel can go 4G internet selected. Tried to remove and put only one micro sim card singtel with microsd memory card still also 3G internet now at my home. Most dual sim phone only support one 2G sim and one sim to be 4G as internet selected since next year april 1 all three telco will switch off 2G network permanently.
But you need to backup data first as if you use fastboot mode any important losses not my problem.
Then try fly gps mock location using facebook, play pokemom go as marshmallow should support fake location as jelly bean not working well.