Hello! I've been working on this issue for quite some time and I am officially stumped. I'm currently running an early 2011 MBP dual-booting 10.6.8 and Windows 10. I would like to downgrade from Windows 10 to 7 but am running into some obstacles doing so. Namely, my optical drive is nonfunctional (spits out every disk I insert) and would need to be replaced. Naively I thought it would be a trivial thing to boot from a USB stick and be along my merry way. Several weeks later I'm reading help pages for GRUB2 when I finally decided to simply ask for help. Is this possible? If so, how? If not, why? Thanks a ton!