I just removed a disk1 from my array using the guide on the wiki.
The guide included emptying the disk to remove, and setting all shares to only include other disks.
I only got 2 disks in (+cache), and after my change I will have 1 disk+cache.
After using the new config function I removed disk1 as I wanted, and then set disk2 as disk1.
Setting disk2 to disk1 caused some problems. All shares were still set to use only disk2, but I didn't have the option to change that. The dropdown for include and exclude disks were both empty, while being marked as "All", but seemingly still only wanting to use disk2, which is no longer present.