Updating CPU microcode possible?

[Nikos Chantziaras]

Hello.

Is it possible to update the CPU's microcode (an Intel CPU, in this 
case) with Grub? Meaning before the operating system starts.

I'm using Grub 2.02 beta 2 to boot three operating systems on my machine 
(Gentoo, FreeBSD and Windows 8.1.) It would be nice if I could make Grub 
do a microcode update before booting any of those operating systems. 
Right now, I am only able to a microcode update in Linux, after the 
kernel is booted.