You can disable or re-enable Tech Support Mode on a ESXi 3.* or 4.0 host by modifying Advanced Configuration parameters.
In ESXi 4.1 you can change the startup services to automatic/manual/disabled or manual start/stop the service.
On the ESXi 4.0 host you need to login with your VI Client direcly or via vCenter server and select your ESXi host.
Click the Configuration tab;
Click the Advanced Settings link;
Click VMkernel in the left-hand pane;
In the list of parameters, deselect VMkernel.Boot.techSupportMode;
Note: Reboot the host before the setting takes effect!