Sure, but you need to modify the script as it requires three firmware files. New released firmwares are now in a single file.
Or you can just use the emui flasher here. It should work.
Hello, I accidentally replaced the update.zip of my P20 Pro by the update.zip of my P10 Plus, so that means the program installed the firmware of the P10 Plus on my P20 Pro, and now my P20 Pro won't start, it's not even alive, when I long press power button or anything, nothing happens, and it was fully charged before it died, looks like the motherboard got completely freezed, what could I do about that ? Should I directly send it to repair ?
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.