I've been wanting to update my displayname in MP but not sure how. I have the Crysis 3 Hunter ED for pc connected with Origin. It's this the Origin ID that I need to update? Also, this is just for aesthetics purposes (capitalization) so would it mess up any stats?

You can change your origin ID no problem, Yes this is what your in game name is, and also it will not mess up any stats
http://www.origin.com/change-id