You would have to extract the files from the iso, replace one of the m2ts files then create a new iso or burn the folder. So, the disadvantage is that you have to do a little work to make it happen, but the major advantage is that you don’t have to re-download 40 GB.
After doing that, should it work as-is or does it need to be rebuilt in some way (multiavchd, bdedit, bdrb, etc)?