Just gave it away.
I have two codes for the same game. Can I register and get coins for them both?
Not on a single account. However, if you really are desperate for those coins, you can set up a family account and link it to your existing account to pool the coins. This allows you to register one game per attached account.
It's actually very, very easy to setup a family account. You just have to remember to check it for the post-play surveys once in a while.