Well, I can't speak for obj, but I have
worked with similar for an fbx exporter script. I had to use MEL
to do it, as the module wasn't available in Python.
FBX has a Mel interface to set its options up, but each module is
slightly different. I can speak to that one from experience, and
probably give some advice, if you're working with FBX.
For OBJ, it stores the preferences in the OBJexportOptions
optionvar. And, just like you showed, it's a string:
"groups=1;ptgroups=1;materials=0;smoothing=1;normals=1". The file
that controls that interface is objExportOptions.mel in your Maya
Install Directory, scripts/other/objExportOptions.mel.
I did find a howto here:
http://ewertb.soundlinker.com/mel/mel.068.php
Basically, though, as stated, it looks to be based on each
available plugin, and each one's slightly different. The options
var basically passes a string of options on to the specified
export plugin.