Installing the needed tools
1$ brew cask install osxfuse
2$ brew install ext4fuse
Mount the disk on your filesystem
1$ ext4fuse /dev/disk2s2 pi-star
Users, groups, write permissions, &c

If you feel that you have to add yourself to another usergroup, then do that as the following code suggests:

1$ sudo dseditgroup -o edit -a $username -t user $groupname