I'm not sure if you're wanting to edit a panorama before you upload it to the site or a true photosynth.
If you are wanting to tweak a photosynth, then I'm not sure what you want to change. Could you please explain what you want to do a bit more?
If you are wanting to edit a panorama before uploading, please try using the Adobe Photoshop plugin that the Microsoft ICE team made: http://bit.ly/pstops
Let me know if this doesn't answer what you wanted to know.