Maybe with Mike's StoreThem program.
http://www.rstools.info/description-3.htmlIt is difficult to find out which assets were installed specifically for a route.
Even if they come with the route, it is possible that you already had them and that removing them will impact another route.
Here is a somewhat tortuous process :
1- Usign 7zip, unpack all the new assets in a different folder or drive, not in your Railworks folder.
2- Copy the files to your Railworks folder using an advanced copy utility like TeraCopy or Syncback. When prompted, say you don't want to overwrite files (or "skip" existing files).
3- When finished, you'll get a report with the status for each file: copied, skipped, etc. The copied ones are the ones you'll want to delete later if you uninstall the route.
4- Find a way to save this information. That's the tricky part, for example TeraCopy offers this function only in its payware version.