I was not clear, maybe...
This function exists in 9.3, so it is possible
Just that if one (I in this case) wants to add a cell to an existing PGC, the new cell will have a new VID (2 if the whole PGC was 1, 3 if it had 1 and 2 and so on). This artificially logically adds a new "segment" - and some other programs interpret this as two parts (like eg main feature and its trailer or studio/authorhouse logo - there are commercial DVDs employing this scheme).
My suggestion was to increase the CID not the VID.
Or alternatively to give me the possibility of setting VID and CID.