Just curious...
When you publish an InfoPath form on to SharePoint, you can select the fields you would like to appear in the form library... Is it possible to a reverse and add more fields onto the form library on SharePoint that automatically updates the InfoPath data source?
It seems like you can read the fields from the InfoPath form but you cannot edit them through the form library datasheet view... and you can only edit the fields which you add from SharePoint only.