From your response, I can only assume you are new to Juniper EX products. I also assume your requirement if some port level security for WLAN/AP network. Do whose switches were you using previously, with this WLAN network? I sort of assume the WLAN is not new, so from which vendor is your WLAN? What was the previous configuration on your old switches?
I assume you are looking to enable DHCP Snooping on a Tagged Interface, which you then want to be untrusted. So under vlans vlan-name forwarding-options you have set dhcp-snooping with set arp-inspection and set overrides trusted. I assume when you then try and add set ip-source-guard, you now receive a commit error?
Maybe you could send your most current config, and what the commit error is?