I recently built an unRAID server (write up is here) using a Zotac 9300 motherboard. I want to change that to a Zotac H55 board and want to know whether I can just switch the boards, plug in the drives, boot, assign them how they were before and have everything run ok. Is this possible? Thanks for your help.

Yep, it should work just fine.  Just take a screenshot of your 'Devices' page and save it somewhere besides the server.  When you boot up with the new motherboard, you will likely have to reassign all your drives to the correct disk slots based on that screenshot.  It is imperative that you get the parity disk correct, because if you assign a data disk to the parity slot and start the array you will loose the data on that disk.  The data disks can be mixed up, though, unRAID will figure it out.  That may screw up your share settings though, so it is best to just assign them exactly as you had them.

Thanks, it worked flawlessly. I'll see about adding the Zotac H55 to the list of working motherboards.

Great, and if possible, please get it to at least level 1 on the motherboard rating scale:

 

Motherboard rating