Try removing yourself from the equation and objectively try to answer these two questions: Why should THEY make an exception for YOU? If THEY were to make an exception for YOU, how many OTHERS should they make the exception for?

One of the reasons they close these types of trails at dusk is to keep ner-do-wells from conducting "business", and pressumably because it is much more difficult to patrol the path than the city streets. Put yourself in the shoes of law enforcement. You could very well be delivering "product" on your bicycle. Are you prepaired to be searched and/or interrogated if caught on the trail after dusk? IMO, that would be a reasonable thing for an officer to do. I might play dumb through the first warning (which you've already had), but I would probably not push my luck for a citation or arrest. I don't automatically have respect for any individual officer of the law, but I do believe that the laws are there [mostly] for our protection whether we agree with them or not. Breaking the law is breaking the law. Are you prepaired to suffer the consequences?

Bright lights front and rear, and increased involvement in your community governance are your best bet.....but that's just my opinion.