What kind of "ammendments"? Do you think that it would be enough to make your SNA app a whole lot better? Definitely a difficult decision... I guess it comes down to whether you'd rather be a NFO or risk having a desk job. I'd stick with NFO if it were me, but you're gonna have to be the one to make the call.
Just ask yourself whether you would be happy as a NFO - if it's yes then I'd say stick with it for sure. If you won't be happy, you probably shouldn't have listed it as a choice on your app. Too late for that, so I really don't know what to tell you. It sounds like a fairly big risk to turn down a slot to OCS and just reapply with a new designator. But then again, if you'll live the rest of your life wishing you were NA instead, it's probably worth the risk.