Yet I turn, I turn, exulting somewhat, with my will intact to go wherever I need to go, (26-29)
There are a lot of things that turn, like werewolves, and Mr. Hyde, and Gremlins. But we don't all turn from good to evil, sometimes we go from good to better. "The Layers" is a poem with forward momentum, despite all the past talk, and the speaker seems to make a switch towards a positive outlook on the future.
no doubt the next chapter in my book of transformations is already written. (41-43)
Wait, so the next phase in the speaker's life exists because it's already written, but it hasn't happened yet? Obviously, the speaker is pretty confident that more transformations are on the horizon. Given that the chronology is out of whack and some other "forces" might be involved, how does he come to this confident conclusion?
I am not done with my changes. (44)
The last line of the poem suggests never-ending transformation. This guy is a transformer, who even in old age, feels like he's got forever ahead of him. They should really make a movie.