No, the headlight housings themselves are a different design and shape. Ford redesigned the front end in 2010. They won't fit at all. Sell the 2009 projectors if you own them and buy 2011 projectors with the money from the sale.
Cutting them apart like the other guy James said is total BS. Don't even bother trying that horrible idea. You'll ruin both pairs of headlights and it'll never work. They'd never seal out water and the reflective coating would flake and peel off the second you take any kind of blade or saw to it. His suggestion is complete butchering of epic proportions. He obviously has never owned a Mustang or any car and actually worked on it.
Yes, its called RETRO fit. You have to cut out your 2009 projector and transplant it into the 2011 headlight housing. You will need to take the 2011 housing apart in order to accurately bolt the projector in.