Go to their website, and go to 'Contact Us' wherever that may be, and Email your ideas. Save a copy of the Email in your Email or hard drive in a place that is dated, and then if they use them without crediting you, you can sue.
Halo 4 has been a mixed bag for me. I mean, it's great, but mechanics are different, and it gets a bit frustrating that it's not uniform with the old games. But, I've never been better with sniping.