I am making an addon, where I have 3D design of bookshelves, but ctm overrides models, so the design is not visible.
Could you add the textures as bookshelf models with different textures, please?

No. We're not changing this just because of one person's add-on.

But why, if it was as models, everyone could use it, not just optifine users, your approach seems so invasive.

We are trying to keep the pack as vanilla as possible, so using custom models is against that idea