manual write of boot code to disk root

[kgrbf]

I've been using this for many many years when I wanted to write boot code to 
the root sector using an off-standard menu file with grub-legacy

Typical example:

grub > root (hd0,1)
grub > install /boot/grub/stage1 (hd0) /boot.grub/stage2 p /WHEREVER/mymenu.boo


It has been working so well that I want the exact analog procedure for grub2. 
The features I need are


the ability to set the menu file anywhere during boot code deployment and the 
ability to edit that file periodically without having to repeat the procedure

the ability to set the disk root where boot code will be written (normally hd0)

How do I do that, preferably with a single direct command line that can also be 
included in a bash script?


TIA