The easy way; since it's new tell em you'll take one WITHOUT the pinstripes. Might as well tell them on the new truck not to prep it that way you can detail it correctly.
Since the title says PAINTED stripes it may just be an enamel which is easier to remove than a catalyzed paint. Is it cleared over as well? Whats is the base color? Solid is preferred vs a flake and white might be the best.
The hard way; since it should be relatively fresh paint break out the sand paper and get to it by hand. Yes you are going to take off some of the surrounding clear coat but take your time it can be done. You can parallel mask the stripe for the begining of the sanding procedure providing maximum CCC protection.
I say take the easy way!