New Mi5c - Settings Not Working. No Real 3g Speed

[SePi82]

When entering *#*#1#*#* and the Telephony when I try to click on Production Target and set to "China Unicom"
it's not working because Production Target is greyed out.

How shall I do that?! Production Target is GREYED out here - I can't change a thing!!!

Every time I switch to LTE TD-SCDMA WDMA through *#*#4636#*#* it keeps switching back!!!
I also tried editing build.prop but it doesn't accept it, either

Sometimes, it shows up 3G/H correctly.. but if you open e.g. Chrome, it switches to E ... ALWAYS!

Why doesn't this work?:

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[SePi82]

Figured it out: this PRODUCTION TARGET Setting is only working on china stable ROM 8.1.10.0. In none of the versions after this one, it's working...
I tried it out in 8.1.10.0 - and it's settable to CHINA UNICOM - and it's weel working with LTE / H / H+ / G ...

The question is: what's exactly the difference? How could we get this working in more recent ROMs? Is it the Song Assistant? (Assistant3.apk)? I can't simply copy it from the 8.1.10.0 because this version is odexed and so not compatible with the deodexed versions...

Any ideas?