I am about submit our game to Mac App Store. What are the code changes I should do to avoid piracy (copy-protection) ?
Are there anything else apart from that I should do (Other than signing my app with their provision profile?) before I submit.
You should validate the App Store receipt.
Note that there is deliberately no code that you can just copy and paste into your app to do this: that's so that each app does the validation slightly differently, meaning crackers can't just patch one single version of the validation code.
There's more information on the Apple developer forums.