Well I downloaded the files for emui 9 163 and made a dload folder with the correct namings. Gonna try to update with usb otg
For the Mate 10 Pro, there are some dload firmware available on androidhost.ru. But, with Pie B108 or higher, dload method doesn't work anymore, but it worked just fine on B106 beta,so probably Huawei fu**ed us... again.
Yes, the bootloader (xloader) will be updated, there's no way around it. Yes, downgrading works, but you will have to factory reset after downgrading.