Can you really make a distributor skip by applying a pencil line between the contacts for the spark plugs?

If the line is dark enough it is possible on an 8 cylinder or even a 6, but on a 4 cylinder engine there will never be two cylinders with burnable mixture ready to fire at the same time. With the ancient Kettering ignition, just the added load of a path to another plug could have been enough to cause trouble but with modern ignitions I doubt it. A path from any of the electrodes to ground (the lip of the cap) is another matter - that is a common failure mode for distributor caps.