ascknd

The following resets the trial license in ESX 6.0

[root@ns3009753:~] rm -r /etc/vmware/license.cfg
[root@ns3009753:~] cp /etc/vmware/.#license.cfg /etc/vmware/license.cfg
[root@ns3009753:~] /etc/init.d/vpxa restart

I then needed to restart ESX to get it to work.

Source: http://esxi.oeey.com/2013/11/how-to-reset-esxi-trial-license.html