Hi,
the vSphere GUIs, Win32 nor the Webclient based on Flash, does not provide the ability to change the label of a license key.
But there is a PowerCli Way. Use the script attached below. Start Powercli and run UpdateLicenseLabel.ps1.
PS D:\> UpdateLicenseLabel.ps1 -vCenter MyVCenter.mydomain.org -key Q1234-2234H-QER49-0234M-85123 -label "My Label" Ok
Michael