Okay, Simon, thanks. I developed a way as well. Because I work with Node I wrote 2 npm scripts: One which copies the original tachyons from node_modules in my static-src/vendor/tachyons-src. The second script then copies from static-src/vendor/tachyons-src to static-src/vendor/tachyons-dev. With this directory I work.
If there’s an update now I run the first script to copy the updated originals into my development environment and then I compare the folders tachyons-src and tachyons-dev with Sublimerge in Sublime Text (or Beyond Compare). Immediately I can see the differences on file level and with a click I can observe the details.
This is part of a test development I’m just doing with Hugo and Gulp to develop a basic theme for our projects. So it’s cluttered at the moment but assumed you can read German you’ll get the hang of it very soon.
Works very well. If you want to clone the repo: https://legobitbucket@bitbucket.org/legobitbucket/hugo-template.git
The main branch is tachyons.
Take care and have a nice weekend.