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

{
    //Get the map's definition
    //Note: needs to be called on the MCT
    var mapDefn = MapView.Active.Map.GetDefinition();
    //Get the Map's Maplex labelling engine properties
    var mapDefnPlacementProps = mapDefn.GeneralPlacementProperties as CIMMaplexGeneralPlacementProperties;

    //Define the abbreviations we need in an array            
    List<CIMMaplexDictionaryEntry> abbreviationDictionary = new List<CIMMaplexDictionaryEntry>
{
    new CIMMaplexDictionaryEntry {
    Abbreviation = "Hts",
    Text = "Heights",
    MaplexAbbreviationType = MaplexAbbreviationType.Ending

 },
    new CIMMaplexDictionaryEntry
    {
        Abbreviation = "Ct",
        Text = "Text",
        MaplexAbbreviationType = MaplexAbbreviationType.Ending

    }
    //etc
};
    //The Maplex Dictionary - can hold multiple Abbreviation collections
    var maplexDictionary = new List<CIMMaplexDictionary>
{
    new CIMMaplexDictionary {
        Name = "NameEndingsAbbreviations",
        MaplexDictionary = abbreviationDictionary.ToArray()
    }

};
    //Set the Maplex Label Engine Dictionary property to the Maplex Dictionary collection created above.
    mapDefnPlacementProps.Dictionaries = maplexDictionary.ToArray();
    //Set the Map definition 
    MapView.Active.Map.SetDefinition(mapDefn);
}

{
    //Creates Abbreviation dictionary and adds to Map Definition                                
    //Refer to the " Create Abbreviation Dictionary in the Map Definition to a layer" snippet above
    //Get the layer's definition
    //Note: needs to be called on the MCT
    var lyrDefn = featureLayer.GetDefinition() as CIMFeatureLayer;
    //Get the label classes - we need the first one
    var listLabelClasses = lyrDefn.LabelClasses.ToList();
    var theLabelClass = listLabelClasses.FirstOrDefault();
    //Modify label Placement props to use abbreviation dictionary 
    CIMGeneralPlacementProperties labelEngine = MapView.Active.Map.GetDefinition().GeneralPlacementProperties;
    //Get the dictionary from the map definition
    theLabelClass.MaplexLabelPlacementProperties.DictionaryName = "NameEndingsAbbreviations";
    theLabelClass.MaplexLabelPlacementProperties.CanAbbreviateLabel = true;
    theLabelClass.MaplexLabelPlacementProperties.CanStackLabel = false;
    //Set the labelClasses back
    lyrDefn.LabelClasses = listLabelClasses.ToArray();
    //set the layer's definition
    featureLayer.SetDefinition(lyrDefn);
}