Downgrade Modem

[gwilly3301]

I'm on the latest Nougat modem for S6 G920t, G920TUVS6FRA3, and I want to downgrade that modem (causing compatibility issues with Oreo AOSP roms I believe) but every time I do try to downgrade in Odin with CP, I'll boot back in and Baseband will be Unknown and I'll have an Unknown IMEI and no data

Is downgrading not possible or will I have to Downgrade something else as well? Like the bootloader?

 

[remocore]

I also need to know this. Anyone please help.