Massachusetts Marijuana Possession

My question involves criminal law for the state of: Massachusetts

My friend was in a car accident recently, not under the influence of anything. A cop searched his car and found some marijuana. We don't know how much marijuana there was. He did not have his stash, so we figure maybe a few leaves at most. Definitely under a gram.

So here's the problem. He needs to set up a court hearing within the next four days. And also, on January 2nd, in Massachusetts, possession of marijuana will be a civil offense (from the recent election). Currently he is being charged criminally for possession of a class D substance.

He is over the age of 18.

How can he turn this into a civil violation when the law changes on the 2nd of January?

I don't see anything in the initiative itself that makes it retroactive. I suggest consulting a local lawyer - you can usually get a free initial consultation - to try to find out how your prosecutor or judge are likely to respond to the change in the law.