Just tried SolviegMM Video Splitter and in the originating VIDEO_TS you end up with the *.mlmix, (name depends on the VOB filename).
When you press the Split button, you're asked where to save the new "chopped" output file, (which defaults to MPEG2 TS format in a VOB), and it'll be called, for example, VTS_06_7_0001.VOB.
You'd then need to rename this to the same as the originating filename and substitute it back into the existing DVD structure, (and hope the navigation still worked correctly), or reauthor a new DVD using it as the source video.