Well, that is somewhat redundant. Most of government is a scam.
Seriously speaking however, yes it is legal for the government to be deceptive. Take a look at the FBI. Their website reads that they use "elements of deception, "intrusion into the privacy of individuals," or they cooperate with people when they know their "reliability and motivation may be open to question." (see comments for FBI website source).
It is legal for police to lie to you, but you can't lie to them. Cops can also pose as drug dealers, prostitutes, etc., to scam people. Instead of capturing real criminals, they take the path of least resistance and snare people involved with consensual activity.
Anyway, you really don't even need anything detailed like that for acting. Why would you? You're on stage or on film. No one can tell. Plenty of stores sell things like novelty police badges.
So, you just made that up. You don't have to make up things to make the government look bad. They look bad all on their own. I guess however, you're looking to buy a fake ID and wondering if you'll get caught. Police are more concerned about shutting down entire operations than catching some underage kid. An entire operation is a big feather in someone's cap. Catching you means nothing for some bureaucrat.