Are ESRI MXD and LYR files read-only? Can you create/write to MXD or LYR files?

Problem/Symptom:
Are MXDs and LYRs read-only in Oasis Montaj/Target, or can you write to them?

Environment:
This resolution only applies to Oasis Montaj and Target v7.0 and the new ESRI MXD and LYR capabilities.

Resolution:
Here is a list of what can be, and what can't be done.

New functionality:
- MXD and LYR files to appear exactly as they appear in ArcGIS with no loss of data quality.
- Like Geosoft Maps, ArcGIS MXDs appear in your Project Explorer.
- They display in a new MXD viewer, and you can open and visualize ESRI MXD and LYR files directly in a Geosoft project.
- Add new group layers
- Delete layers
- Add shapefiles through the Add Data button (similar to the Add Data button in ArcGIS).
- Change the view of the MXD and save it for use in ArcGIS.
- (You can still create SHP files from within Oasis, through the Map > Export feature, or by exporting from a Geosoft database to SHP file.)
- Cursor tracking and dynamic linking exists between MXDs and Geosoft Maps.
- MXD files may be saved as Geosoft Maps and Geosoft Maps may be saved as MXD.
- Ability to drag and drop layers from MXDs directly into Geosoft Map groups, or from Geosoft Map groups into MXDs. This would include SHP and LYR files. Thus, you can take a LYR file from your Geosoft map and drop it directly into an MXD, and save that new MXD.

The following will not work:
- Cannot access the properties of individual layers in an MXD
- Cannot create SHP or LYR files in the MXD viewer