From Alex Plumb on superuser:

If you're comfortable with using the Terminal, try this:

First, look at the partition table by running this command:

diskutil list

You should see something like this:

0: GUID_partition_scheme *16.0 GB disk1
1: EFI 209.7 MB disk1s1
2: Apple_HFS Example 15.7 GB disk1s2

The partition we want to change is /dev/disk1.

We want to change the device to an MBR-formatted FAT32 partition.
To do that, run this command:

sudo diskutil eraseDisk FAT32 NAME< MBRFormat /dev/disk1

where NAME is the name you want to give to the disk.

As mentioned in the comments, you cannot put square brackets into the volume's name lest things mess up. To avoid having everything fail, simply ensure that there are no square brackets in the FAT32 volume's new name.