Yes, EXTREMELY carefully. I think that your instructions, although incredibly thorough, applicable, and above all useful they may be a little too advanced, judging by the volume of "Man! Me, too!" posts. I'm not trying to sound harsh or anything, I just read so many of, "MacBook Pro checking in, same here!" posts that flooded the thread with nothing useful to report that when I figured it out, I felt insulted. It's almost as if the simplest solutions have been hidden on purpose.
As far as the EFI and its interaction with GRUB goes, this is what worked for me..
1) If you get to the GRUB menu, but get an error like, "file system not recognized," edit that boot option to say...
2) Instead telling GRUB to read from (hd0,1), change it to (hd1,1)
I always remind myself that GRUB doesn't use the same "language" that we're all used to, being Linux users. I don't wanna seem preachy or anything, long day.. Anyway, I just think, "/dev/sda = (hd0,1), so if I'm using a USB to boot from, then /dev/sdb = (hd1,1)". I hope it helps someone else out there, and if this was actually proposed as a solution and I missed it, my bad.