I also did the same. I joined my existing rom set to the split torrent and it updated, but I did also download the smaller torrent7z merged set so I have both sets, because I think they will end up going the 7z route for all sets, but whilst they are still supporting the split set I wanted to continue being able to seed it back to help others downloading.

And I also started again with the complete CHD set. It was too complicated and time consuming to try and rebuild the older set to join the next set.

They don't seem to have released the 0.147 extras set yet though.