Ability to update categories on a post without fully re-knitting?

[mikemc]

I would love the ability to easily edit the categories/tags of a post (and ideally other post frontmatter like the title, authors, and description) without needing to re-knit the Rmd file (and thus having to re-run the R code). Basically something like a update_categories() or update_frontmatter() function that updates the relevant part of the html and file and updates the _site/ folder like a call to knitr::render() does, but without processing any of the non-yaml part of the Rmd doc.

Any chance something like this might be implemented? Or perhaps there good reasons I'm not thinking of why it would be a bad idea?