Law Changed and Charged with Old Law vs. New Law

My question involves criminal law for the state of: Idaho

So this is a little silly. But I have a city code misdemeanor offense pending against me regarding a sign on my property. They investigated it in 2010 and gave me a warning on an abandoned sign issue. I said it didn't apply to me as it didn't. Then in Feb. of this year the city changed the city code. Now I just got a summons for a misdemeanor charge for a different sign offense (off premise sign) referring to the city code as it was in 2010 and not the 2011 code as it is now.

Can they do that? Don't they have to charge me with the current law vs. the law in 2010 when they said this offense occurred? Because now it's an infraction in the new code vs. a misdemeanor as it was in 2010. Also the complaint refers to the old code sections and not the new code sections which seems like incompetence on the prosecuting attorney. I just don't want a criminal record for something so ridiculous as this.

The law that applies is as it was in effect at the time you committed the offense.
It's actually unconstitutional to charge you with a law enacted after the offense.