"^has_journal" switched it off, "has_journal" will switch it back on. The tune2fs command allows you to change options on a file system that already exists.
To disable journaling:
sudo mke2fs -t ext4 -O ^has_journal /dev/sdb1
To (re)enable journaling:
sudo tune2fs -O has_journal /dev/sdb1
The dumpe2fs command will let you see the state of the file system:
sudo dumpe2fs -h /dev/sdb1