I'd try it with GPARTED, a bootable standalone tool for such work.

However I don't think Android will take to such a card.

I see you tried it with GPARTED so my thought is this is not supported at all.

Also, since I do write Android apps, why would I need this? Here if I need a space on the SD card, I create a folder and the files go there.

TL;DR. I use folders.