A good method for creating new templates like this is to make the desired configuration change directly on a test device's web GUI and then export the configuration to use as a baseline.
If the test device is managed cnMaestro you can go to Configure -> Devices, find that device and click the page icon under the View column. This will display the device's confguraiton as a template which you can save from that view.
If the test device is not managed by cnMaestro, on the device web UI navigate to Configuration -> Unit Settings -> Download Configuration File and click the link with the format <MAC address>.cfg. The downloaded file can be used to create a template.
I sometimes use a text editor for this part. Search the text of the template for the VLAN entries you are interested in and remove everything else. Most of the parameters should have 1-to-1 matching with what you set in the web GUI. When you are done editing, validate the template using something like http://jsonlint.com/ to ensure the format is still correct.