Your request is not a new one, but no, Photosynth does not currently offer any image editing capabilities for stitching errors.
You would need to use something like the panorama publishing plugin for Photoshop to upload edited panoramas to Photosynth's website. You can read about it and get the download link here: http://bit.ly/pstops I should warn you in advance that it is not really designed with editing panoramas from the mobile app in mind. What I would do is to use iTunes to sync the input photos for your pano to your PC, use either the free Microsoft ICE panorama stitcher ( http://bit.ly/microsoftice ) or Photoshop Photo Merge to automatically stitch the pano to a layered Photoshop file (you'll find this in ICE's dropdown list of export formats), then edit the pano in Photoshop to your heart's content before uploading to the Photosynth website. Here's the official Photosynth weblog about the Photoshop plugin: http://bit.ly/pstops-wlps