There was another member local to me who I heard was heading in to have the tail light replaced for a 3rd time also, and I was about to advise him to perhaps consider to Lemon... But then I took that idea back because it really and truly may not be worth the mental hassle and time away from truly enjoying this great sports car... This is the truth, I feel.
OP, I completely understand your frustration... Just let it go, and let Toyota go ahead and cure the situation, and make sure that they attend to it accurately this time around by perhaps keeping in touch with Scion's Corporate Office in order to make sure they're with you all the way on this specifically. I'm very positive they want to make certain that you're happy at the end... Just give them that chance.
Don't let this minor issue which has popped up a few times get in the way with your ownership experience... It's not worth stressing over, and I hope you will indeed give the car a opportunity to be enjoyed thoroughly through its life with you. My FR-S has some small issues, as well... But I'm afraid of sacrificing even a day of my ownership due to being in the dealer's service shop... I'd rather enjoy it fully, despite the first-year hiccups. And I already know that I will likely trade-up for an updated version / model year later down the road anyway. For now, this car is meant to be enjoyed, and I hope you will feel the same way too.
All the best,
frsinpa. 