Depending on what it’s authored on it can be done. Sonic Solutions uses a technology they developped called “Open DVD” which allows DVD to be reedited as needed without going through the whole remux process.
If not, then perhaps ripping it, and reautoring with an offset may work. Youmay want to try a facility that does autoring profressionaly as a service. Give PostWorks a call on 100 6Th Avenue as a start.
Michael