Some filters I've written to modify Pandoc 1.8 documents. Includes support for Beamer presentations, labels for Latex figures and SyntaxHighlighter support for code in HTML documents. Some of the filters are working, but others are still work in progress. For more info on Pandoc filters see John MacFarlane's instructions.
And here is how you can use the filters:
pandoc -t json textfile.md | runhaskell filtername.hs | pandoc -f json