I was able to do it, though I don't fully remember what I did cause it was a stressful situation. I did have an issue at first where I had two nodes showing up in GUI, one with old hostname, one with newhostname but without anything working.... then I went through and changed everything I could find that referenced the old hostname to the new hostname.
Here are the files I changed and procedures I took that I can think of:
On the host which name you want to change:
/etc/hostname - make sure hostname is name you want
/etc/hosts - make sure hostname is name you want
/etc/pve/corosync.conf - make sure hostname matches
Then make sure folder located in /etc/pve/nodes which reflects old hostname is moved to the new hostname.
Eg:
old hostname = nodename12, folder name = nodename12
new hostname = newName32, folder name = newName32
I only have a 2 node cluster, and I did this for both hosts (may not be necessary?)
Then you will have to get the new SSH key by the known method of ssh from a node in cluster to the new host name, or else it won't connect either.
Since I lost quorum it was a bit trickier to do all this, but maybe it should be easier for you.
edit: I also restarted the host, and when I did everything "correctly", it worked. So yes, it IS possible, but may be a bit scary if you don't do everything necessary first =D
