public enum UnitFormatType : System.Enum, System.IComparable, System.IConvertible, System.IFormattable, System.ISpanFormattable  

//Must be on the QueuedTask.Run()

var unit_formats = Enum.GetValues(typeof(UnitFormatType))
                      .OfType<UnitFormatType>().ToList();
System.Diagnostics.Debug.WriteLine("All available units\r\n");

foreach (var unit_format in unit_formats)
{
  var units = DisplayUnitFormats.Instance.GetPredefinedProjectUnitFormats(unit_format);
  System.Diagnostics.Debug.WriteLine(unit_format.ToString());

  foreach (var display_unit_format in units)
  {
    var line = $"{display_unit_format.DisplayName}, {display_unit_format.UnitCode}";
    System.Diagnostics.Debug.WriteLine(line);
  }
  System.Diagnostics.Debug.WriteLine("");
}

//Must be on the QueuedTask.Run()

var unit_formats = Enum.GetValues(typeof(UnitFormatType))
                      .OfType<UnitFormatType>().ToList();
System.Diagnostics.Debug.WriteLine("Project units\r\n");

foreach (var unit_format in unit_formats)
{
  var units = DisplayUnitFormats.Instance.GetProjectUnitFormats(unit_format);
  System.Diagnostics.Debug.WriteLine(unit_format.ToString());

  foreach (var display_unit_format in units)
  {
    var line = $"{display_unit_format.DisplayName}, {display_unit_format.UnitCode}";
    System.Diagnostics.Debug.WriteLine(line);
  }
  System.Diagnostics.Debug.WriteLine("");
}

//Must be on the QueuedTask.Run()

//UnitFormatType.Angular, UnitFormatType.Area, UnitFormatType.Distance, 
//UnitFormatType.Direction, UnitFormatType.Location, UnitFormatType.Page
//UnitFormatType.Symbol2D, UnitFormatType.Symbol3D
var units = DisplayUnitFormats.Instance.GetProjectUnitFormats(UnitFormatType.Distance);

//Must be on the QueuedTask.Run()

var unit_formats = Enum.GetValues(typeof(UnitFormatType))
                      .OfType<UnitFormatType>().ToList();
System.Diagnostics.Debug.WriteLine("Default project units\r\n");

foreach (var unit_format in unit_formats)
{
  var default_unit = DisplayUnitFormats.Instance.GetDefaultProjectUnitFormat(unit_format);
  var line = $"{unit_format.ToString()}: {default_unit.DisplayName}, {default_unit.UnitCode}";
  System.Diagnostics.Debug.WriteLine(line);
}
System.Diagnostics.Debug.WriteLine("");

//Must be on the QueuedTask.Run()

//UnitFormatType.Angular, UnitFormatType.Area, UnitFormatType.Distance, 
//UnitFormatType.Direction, UnitFormatType.Location, UnitFormatType.Page
//UnitFormatType.Symbol2D, UnitFormatType.Symbol3D
var default_unit = DisplayUnitFormats.Instance.GetDefaultProjectUnitFormat(
                                                     UnitFormatType.Distance);

//Must be on the QueuedTask.Run()

//UnitFormatType.Angular, UnitFormatType.Area, UnitFormatType.Distance, 
//UnitFormatType.Direction, UnitFormatType.Location

//Get the full list of all available location units
var all_units = DisplayUnitFormats.Instance.GetPredefinedProjectUnitFormats(
                                                      UnitFormatType.Location);
//keep units with an even factory code
var list_units = all_units.Where(du => du.UnitCode % 2 == 0).ToList();

//set them as the new location unit collection. A new default is not being specified...
DisplayUnitFormats.Instance.SetProjectUnitFormats(list_units);

//set them as the new location unit collection along with a new default
DisplayUnitFormats.Instance.SetProjectUnitFormats(
                                        list_units, list_units.First());

//Note: UnitFormatType.Page, UnitFormatType.Symbol2D, UnitFormatType.Symbol3D
//cannot be set.

//Must be on the QueuedTask.Run()

var unit_formats = Enum.GetValues(typeof(UnitFormatType)).OfType<UnitFormatType>().ToList();
foreach (var unit_type in unit_formats)
{
  var current_default = DisplayUnitFormats.Instance.GetDefaultProjectUnitFormat(unit_type);
  //Arbitrarily pick the last unit in each unit format list
  var replacement = DisplayUnitFormats.Instance.GetProjectUnitFormats(unit_type).Last();
  DisplayUnitFormats.Instance.SetDefaultProjectUnitFormat(replacement);

  var line = $"{current_default.DisplayName}, {current_default.UnitName}, {current_default.UnitCode}";
  var line2 = $"{replacement.DisplayName}, {replacement.UnitName}, {replacement.UnitCode}";

  System.Diagnostics.Debug.WriteLine($"Format: {unit_type.ToString()}");
  System.Diagnostics.Debug.WriteLine($" Current default: {line}");
  System.Diagnostics.Debug.WriteLine($" Replacement default: {line2}");
}

//UnitFormatType.Angular, UnitFormatType.Area, UnitFormatType.Distance, 
//UnitFormatType.Direction, UnitFormatType.Location
var angle_units = DisplayUnitFormats.Instance.GetProjectUnitFormats(UnitFormatType.Angular);

//Edit the display name of each unit - append the abbreviation
foreach (var unit in angle_units)
{
  unit.DisplayName = $"{unit.DisplayName} ({unit.Abbreviation})";
}
//apply the changes to the units and set the default to be the first entry
DisplayUnitFormats.Instance.SetProjectUnitFormats(angle_units, angle_units.First());

//The project must be saved to persist the changes...