Question about custom kernel, NVRAM edits and OTA updates - Xiaomi Mi CC9 / Mi 9 Lite Questions & Answers

Hello everyone!
I have a Mi 9 from China, which is running Xiaomi.eu ROM 20.1.21 and is rooted with Magisk 20.3 and I have TWRP 3.3.1-46 as custom recovery.
My device does not have Band 20 unlocked. My carrier uses Band 20 for LTE, so I would like to have this band on my device as well.
My girlfriend has a Mi 9 from the Netherlands (where we live), which does have Band 20, so it should be possible to unlock band 20 on my phone, since the Snapdragon 855 does support this band.
I read somewhere on this forum (here) that the bands are locked somewhere deep in the system and that it is possible to unlock them by changing values in the NVRAM.
There is a very big chance I'm going to need a custom kernel to be able to write to the NVRAM, because apparantly Qualcomm added some anti temper software to prevent unlocking extra bands (and other features).
I also read somewhere (here) that every OTA update from Xiaomi.eu ROMS installs a new original kernel.
With this information, I have the following questions:
- Do I need a custom kernel to edit the NVRAM to unlock band 20?
- If I do need a custom kernel, which one whould you advise?
- If I have a custom kernel, can I still update my Xiaomi.eu ROM through OTA?
- If I can update through OTA, will the changed settings to the NVRAM remain there, or will the newly installed kernel also reset the values (and I will lose Band 20)?
I would really appreciate your help!

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saurabhcfp said:
I by mistake through short cut master lite app changed the radio band to United States.... since then I am not able to get network on one of my sim....have tried swapping sim ....even downgraded the firmware ....but still the band is stuck at USA......ONE Plus 3T is currently on oxygen OS Nougat beta version.....Someone in this forum suggested to flash modem zip .....can anyone provide modem zip and the procedure to flash it which can reset my radio band settings ...build no is ONEPLUS A3003_28_161229.....The phone is ONE PLUS 3T 64 GB
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You can find them all here
https://forum.xda-developers.com/showthread.php?t=3509015
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