i generally don't trust anything anyone at the stealership says.
what is it that you're trying to do nate? you wanna add another link onto your chain? if so, i gotta agree w/ the stealer on this one....but for more reasons than he said.
if it's a clip type master link, it is the weakest link in the chain....even though clip masters are actually pretty strong. so if you've got 2 clip links in a chain, you've got 2 weak spots. chains do break, i've broken one and i've seen a bunch of em break, no reason to make it weaker than necessary.
also, you want the chain to be as short as you can get it to be because they stretch. when you install a new chain, you want to push your chain adjusters all the way forward so that carrier is pushed forward. then install the chain, removing any links that you can. this way, you'll have the most travel for the chain to stretch.
unless you're trying to extend your swingarm or put on a larger sprocket.
either way, i would recommend getting a new chain w/ the proper # of links.