Actually, 2nd gen Frontiers don't have any stripes. Anything you have seen beyond the NISMO/PRO4X are dealer installed. A single or double pin stripe is quite easy. It just takes a little practice. You can pick up a roll at most auto parts stores. I recommend you stick with 3M brand stripes. They are not that expensive, so, if you mess up, pull it back off and buy another roll.
Clean the vehicle with a automotive wax remover. Stick an end at the starting point allowing enough to make a point, unroll enough to cover the panel you are working on, hold it tight, and slowly lay it onto the vehicle. Lightly pat it in place. Pull a little back up to start the next panel and repeat until finished. Press the stripe firmly to the vehicle except the very front (if you wish both stripes to come together to a point). Remove the clear layer, pull the top and bottom stripe back far enough to make the point you want, lay it back down, press firm, trim the excess and the joints between each panel, and you are on your way to making a few $$$ on the side.
Sounds like a lot of work, but once you have done it a couple times, it is real easy. And the dealers charge as much as $300 for a simple stripe.