I do merge sets. Zip those up using the clrmamepro. Drop those zips into the trrntzip64 for a repacking smaller size. I use a frontend to find the clones. Risk free here and less work. Recommended.
I stop using the T7Z for a reason. The reason is the softwarelist and sometimes the clrmamepro will damage the T7Z when repacking the ROM's. If you want to use the T7Z instead of ZIP. That is a lot of work on repacking and there is a risk chance to corrupted your sets. torrent7z can check your sets for a corrupted T7Z. Good luck on this part. There always a risk. Not Recommended.