Can you limit the fields that are available for editing by user in collector?
Try this: in the MXD that you will publish as your editable feature service, set the fields you don't want edited to "Read-Only" (Layer Properties - Fields Tab - Read-Only).
I haven't actually tried it but generally feature services honor the settings made in the published MXD. So, I suspect this will get you there.
If you are using web app builder developer in the edit widget config you can choose which fields are editable. If your map is hosted on arcgis online then under popup configure attributes you can select which fields you want editable