Does grace mean Christians can live however they want, like the devil's crowd?
No. Grace is not licensed, so it does not permit believers to live like the devil's crowd. The true believer does not want that lifestyle anyway; their desires are totally different. As the context illustrates, a genuine believer would be as miserable in a honky tonk as a honky tonk customer would be in church.
Les explains that salvation rests on Christ doing all that was necessary, so the believer does not have to work and sweat and worry, hoping to have done enough. But Les is careful to repeat that grace is not licensed. It does not mean a person can go out and live like the devil's crowd, mostly because the true believer does not want to. Les illustrates this by saying the average true believer would be as miserable in a honky tonk on Saturday night as a regular honky tonk customer would be miserable in church on Sunday morning. It is two totally different lifestyles and desires. This fits the contrast with Moses and the abolished system of Law, replaced by the revelation of the mysteries, the grace of God.