That link talks about getting a disk to mount. This one already does that, it just won't let me write to it. And it was working fine yesterday, so something changed. I will try the Disks app again later (no luck there yesterday, though) when the usb dock is not being used to backup my Windows partition; right now I can't insert the funky disk. More later.
EDIT: just inserted it again and it let me write to it once. I have changed literally nothing since yesterday. I wonder if the disk itself is getting wonky. This is certainly not consistent behavior! It let me copy a file to it, but it won't let me delete the file once it's copied. This seems strange. And now once again it says the disk is read-only.
Going into Disks, I see that compared to the mount options shown in your link (users,noexec,nosuid), mine says nosuid,nodev,nofail,x-gvfs-show. Is this important? I left it the way it is until I know more about what I'm messing with. After saving the Disks changes the drive is still mounted but still also read-only.