Send and receive sysex messages via Renoise API:
http://code.google.c…ippets/Midi.lua
Using the “Document API” to create persistent settings (in this case, to build a library of sysex dumps)
http://code.google.c…ocument.API.lua
I think the biggest challenge with a project like this is not the MIDI communication itself, but rather to maintain the persistent documents/settings. Unfortunately, the Document API is kind of tricky to work with - but then, as you just pointed out you’re not alone with this project 
Also needed is a good way of matching a particular song with particular preset(s). BeatSlaughter has done some groundwork with his Mixer Utilities tool, which will simply save a special file next to the song telling the tool that “this particular song has some customized settings”. Perhaps the same approach could be applied to this tool?