Mount a ext4 partition on Mac OS X
I have found a solution couple of month ago. I bought this one https://www.paragon-software.com/home/extfs-mac/ and it works like a charm. And I didn't have a chance to find any free solution. ext4fuse is fine but for read-only mode.
It seems it isn't currently possible.
A possible workaround for some scenarios is explained at http://www.cyberciti.biz/faq/mac-os-x-read-ext3-ext4-external-usb-hard-disk-partition/
Try MacFuse with ext4fuse. If you want it to be risk-free, mount it read-only or duplicate the partition first.