Haha, I'm glad I'm not just amusing myself.
[Well, excuse him for caring!1 Assuming Sebastian wants to lessen the constriction of the dress is logical, yes, but right now Sebastian is more focused on undoing whatever magic is trying to hide Ciel from him, and Sebastian's problem-solving approach isn't always to take the most logically obvious route (besides, clearly someone has to care about Ciel's womanly modesty). He reaches out to unclasp that new necklace of Ciel's, letting it unceremoniously fall to the ground and shatter if it so pleases, after which he goes for the new studs in Ciel's ears. Remove new strange things = everything goes back to normal??
(Let's take a moment to appreciate that his trying this means Sebastian just accepted his own new accessories when they showed up and never even bothered trying to take them off despite the annoyance of his sudden power downgrade.)]