What metadata specifically are you worried about? Camera data should be the same for all copies of the image including VC's as should capture date/time (unless we're talking about scanned images). Other metadata like title, caption, keywords, country, state/province, city etc. can be different on the master vs. any VC's created from that master. If you convert the VC to be the master the VC's metadata should come along with it as seen in LrC and the metadata from the old master will follow that version now known as a VC.
But, again this is only information kept in the LrC catalog. If you then want the metadata from the new Master to also be on the phyisical file rather than the metadata from the used to be master then you need to save metadata to disk which should over write the prior masters informaton with the informaton from the VC which is now considered the master in LR. If that makes any sense - or was even your question
Dan