[ffooky]

If you're trying to replace a VTS_* in a VIDEO_TS folder that has other VTS sets like a menu etc then you'll have to rename at least the VOBs created by ffmpegX to match the originals, maybe the VTS_0*_*.BUP/IFOs as well and try just dropping them into your original VIDEO_TS folder (saving the original VTS beforehand of course). I imagine that'll only work as long as the times/codecs of the replacements match the originals. If not then you'll have to try reconstructing the whole shebang with something like MovieGate.