I have an Rmd file with a lot of cached code chunks.
Now I want to keep developing that script using an interactive session to play around and test diff
I think that running library("knitr"); knit("foo.Rmd") in the console/R session is the easiest way to do this, although it will rewrite foo.md, figures, etc.. (Too busy/lazy to test it at the moment.)
You could probably poke around in the cache directory and read the cached files directly, but that would be a lot more work/trickier.