jQuery Grid Plugin - jqGrid

Hi.. I am really new with this !!!

and.. I am trying to tweak a lil the basic forms

I was reading a lot for comments here but I didn't find nothing for my case

I have this part of code for my table table

….

colNames:['Deployment id','Branch', 'Release Name','Client id','# of hosts','Comments',''],
colModel :[

{name:'deployment_id',index:'deployment_id',align:"right", sorttype:"int", width:120},
{name:'branch',index:'branch',align:"center", editable: true,edittype:"select",editoptions:{value:"1:valor1;2:valor2;3:valor3"}},
{name:'release_name',index:'release_name',align:"center"},
{name:'client_id',index:'client_id',align:"right", sorttype:"int", width:60}, {name:'num_hosts',index:'num_hosts',align:"right", sorttype:"int", width:60},
{name:'comments',index:'comments',align:"center", editable: true,edittype:"textarea", editoptions:{rows:"2",cols:"20"}},
{name:'myac', width:80, fixed:true, sortable:false, resize:false, formatter:'actions',formatoptions:{keys:true}} ],

….

I need modify my edit/add dialog form in order to

When I add: Branch and Comment are available

When I edit: Only Comment can be modified

How I can know When I am Editting or Adding? in both cases are usign the same function "editGridRow"

In addition.. It's possible to get the options values in my Branch name from JSON? or a simple list? How i Can modify the editoptions for that?

Thank you