Ah hah! I knew that if I stepped away from it for a few hours, I'd probably calm down. Despite the fact that those few hours served to tear my heart in another way, at least my Photoshop-inspired hate ebbed, and I managed to get as far as Step 38. I've selected the Mountains layer, and Ctrl + Click 'd the Change layer, but it won't let me Modify. The option's unselectable. Ideas?

(And I hope everyone knows I'm not mad at any of you; in fact, I'm quite grateful. It's only that things have always come naturally to me, and I've been able to grasp the concept on many, many things fairly quickly. When I don't, it hurts.)