I can see where you're coming from there, for sure as far as re-adding the title, tags, description, setting the license again, and remembering to choose the desired thumbnail again.
If you still have the synther open from creating the first test version of a synth, you can actually do the trick of right clicking on the title there in the list of completed and pending synths and choose 'Edit'. This will keep all the items I listed in the first paragraph of this post the same and allow you to add or delete photos from the new version of the synth (although it will still be a separate synth from the first). The nice thing about doing this is that the upload won't repeat for any photo that is exactly as it was when used in the first synth. Only new photos which havan't been used in a synth before or modified versions (crops, rotations, added or removed EXIF tags, etc.) of photos will be uploaded with the point cloud and 2D layout file the second time.