Hi - Have you tried implementing the approach suggested by ?
I was having the same similar issue with an expired (evaluation mode) license on my ESXi Host, and after renewing the Eval license, my vCenter did not wanted to re-connect my ESXi Host. It kept giving me this error when trying to reconnect: "Reconnect host failed! Cannot complete the license assignment operation "vCenter agent for VMware host" The Evaluation Mode license on "Host" esxi1.jdfvmshop.local cannot be changed".
The easy solution that resolved my disconnect and re-connect issue was to:
- Login to the vCenter Server.
- Right-click your Disconnected Host and remove from inventory.
- Using the vCenter menu and Workflow (wizard), go to Actions --> Add New Host.
- The Add workflow will give you the option to add the Evaluation License to your previously disconnected ESXi Host.
That's it.
PLEASE NOTE: I am using a Nested environment, so pay attention and assess your own environment to eliminate any impacts on your VM's and Clusters (if available).