You're on the right track as far as fire-eaters steering Southern citizens into conflict with the North. Exactly how did this relatively small group with little poiltical influence up until the late 1850s manage to co-opt the Southern states during the election campaign of 1860? It's an unsolved mystery.

Let's say that we're talkling about firearms instead of slaves. For the sake of argument, let's say that Mayor Fernando Wood pursuaded New York to join the Confederacy. The Confederate Constitution says that regardless of the laws governing firearms in New York, you as a visitor may carry a firearm, concealed or otherwise as you please. In effect the laws of New York on this subject are null and void. Article I Section 9 already guaranteed the right of any citizen to own slave property cannot be abridged, so citizens of New York could own slaves. To cover all the bases, the rights of a traveller to bring slaves into the state could not be restricted, either.