You can use wszst to unpack and re-pack SZS files and wit to unpack and re-pack ISO or WBFS files.
https://wit.wiimm.de/ and
https://szs.wiimm.de/
"wit extract image.iso folder/" to unpack an ISO, "wit copy folder new-image.iso" to create a new ISO from the folder.
"wszst extract Common.szs" to unpack the Common.szs, "wszst create Common.d -o" to re-pack it to an SZS file.