If I did it without -t, or with -t latex, it will support highlighting.

Currently highlighting is supported only for HTML, EPUB, Docx, Ms, and LaTeX/PDF output.

Is there a way around this?

Otherwise, can I convert all <pre><code> blocks to HTML blocks, highlight them with Prism.js, and convert back to PNG?

I found this, but couldn't make sense of it.

Why ConTeXt? It seems to be the only way I can,

• Change paper size mid-way
• Easier to centering vertically