Yes, you can cut off the metal part and the cable will work. It's just a piece of bendy metal wire that's next to the main wire, then wrapped in a tubing. Cut the tubing carefully then snip off the metal wire.
I don't think there are any replacement cables made by anyone else besides KZ. If you need the mic, the stock cable w/mic is the only choice you have.
While the pins are standard UE 0.75mm pins, the housing unfortunately is KZ specific (and even earbud specific, as the ZST cable won't work on ZS3). Here's hoping the ZSR (and other future KZ earbuds) use MMCX standard connectors...
Update: I removed the metal wire and the tubing and I love the ZS3s even more now! They are a steal at $10.