You can change the edition options before editing a row.
$('#dg').datagrid({
onBeforeEdit:function(index,row){
var col = $(this).datagrid('getColumnOption','productid');
col.editor = {
type:'combobox',
options:{
data:[{
value:'Red',
text:'Red'
},{
value:'Blue',
text:'Blue'
}]
}
}
}
})