I created an ISO 19139 metadata template. Before I imported it to test it I noticed I couldn't edit it at all. On the top of the editor in ArcCatalog on the description tab there is usually a choice to print, edit upgrade or import the metadata.
On the template I created there is only a choice to print or import the metadata.
I also tried importing it and nothing changed.
I've had the same experience - you can't edit ISO 19139 metadata from within the ArcCatalog (I'm using Arc 10.2). You select a metadata profile that you want to use, and when creating the metadata in the catalog is saves it in the ArcGIS metadata format. Then you export your metadata using that profile (i.e. to ISO), and can validate the ISO record against a schema using tools in the ArcToolbox. If you need to make changes, you either go back to the ArcGIS metadata, change, and re-export (so you always keep two copies of the metadata records around) or - you use an external editor for the ISO records.
From the most recent help docs here: http://desktop.arcgis.com/en/desktop/latest/manage-data/metadata/the-arcgis-metadata-format.htm
Midway down the page:
"If an item has existing metadata content that is not in the ArcGIS metadata format, the current version of ArcGIS for Desktop can't use that information. For example, the ArcGIS metadata editor and the Export and Validate buttons only work with content that is stored in the ArcGIS metadata format. When you use the Import button, the metadata content you are importing is converted to the ArcGIS metadata format. "
The answer you received from @fdonnelly is on the dot. ESRI uses their own metadata template, which comprise metadata elements from several metadata standards (FGDC, ISO, Inspire, etc). The idea is to provide a catch-all-needs style, which has two key features:
You can always export your metadata into a standard format (for instance ISO19139), effectively filtering it out to the contents of the standard you need.... but the exported version will not be editable any longer... but you do retain the original, ArcGIS-style, editable version.
See it as your work copy, continuously updated as you data change; whereas the export is your well-formatted deliverable.
Our office looked into the mecanism under the hood - the metadata is encoded differently between the ArcGIS metadata style and the standards styles (like ISO19139). Direct consequence: the XML file you can generate will have a different structure, notably different tag names and organisation, and different content (ArcGIS-style XML will contain more than a ISO19139 XML). This is easy, and (but) does not explain the fact that standard metadata is read-only in ArcGIS.
As we were told by our local ESRI rep, the ArcCatalog metadata editing interface is tightly bound to the ArcGIS-style structure, and is therefore limiting when you want to work with other metadata styles or standards: it is (probably) easier for ESRI to design a conversion process, using a series of XSL files, between the ArcGIS metadata file and its ISO19139 equivalent, than to recode their interface for the various metadata standards they support.
The answer I am getting through a lot of research on the internet is that you can't edit ISO 19139 data in Arc GIS 10.x. The only issue I have is that this answer was written in 2012 and I can't confirm that this is still the case.
