in your layerInfos set 'isEditable': false
To be more specific, if you want certain attribute read-only, set the layerInfos isEditable to true, and set fieldName isEditable to false.
var layerInfos = [{
'featureLayer': selectedTemplate.featureLayer,
'isEditable': true,
'fieldInfos': [
{ 'fieldName': 'STN_NAME', 'isEditable': false, 'tooltip': 'Station Name', 'label': 'Station Name:' },
{ 'fieldName': 'SITE_NAME', 'tooltip': 'Site Name', 'label': 'Site Name:' },
{ 'fieldName': 'STN_TYPE', 'tooltip': 'Station Type', 'label': 'Station Type:' }]
}];