Someone asked me fairly recently about how I use theme.
For me, I might think about theme ahead of time, but it doesn’t really start to manifest until I’ve written a certain amount of the manuscript. Then I start realizing what my subconscious is trying to tell me (or maybe my conscious mind gives it a name and a shape). Like, for The Moonlight Mistress I knew wolves were a symbol of the wild, but linking the shapechanging idea to the human characters sank into my my mind gradually, influenced by something a transgendered woman had once told me about feeling she was a real-life shapechanger.
I decided that acting outside of conventional gender roles was also, in a way, like shapechanging, and I had plenty of characters who did that, whether by dressing and acting as the opposite gender, or performing a job usually associated with the other gender, or simply by not having a heteronormative sex life.
After I realized all that is when I start adding descriptive details throughout the manuscript to emphasize this theme and to, hopefully, bring the idea to the reader’s attention. I examined all the characters and how I’d presented them, and thought about which ones were most like shapechangers, and how, and tried to emphasize that a little, indirectly. I also tried to do a little bit of mirroring, werewolves with humans.
I don’t know if that kind of detail actually works for the reader or not, but I make the attempt. Even if it doesn’t come through, it’s fun to do! I’m also not sure if it really counts as theme if you’re doing it on purpose. But I think it should count.
I’m still thinking about this myself, so I apologize if I sound a little vague. Your input is welcome!