Any way to edit MSR registers under Haiku?

I’m used to running wrmsr on other OSes. Compiling the linux version from github doesn’t work because the program is hardwired to use /dev/cpu , which obviously doesn’t exist on Haiku.

Is there any way to edit msr on haiku without using bootloaders like grub?

I can’t answer it but I can point you to

Hmm, I don’t think we expose this to userland yet.
You could have a look at the poke driver which exposes IO and other things to userland. see src/add-ons/kernel/drivers/misc/poke.cpp.