來自：https://community.esri.com/t5/arcgis-pro-sdk-questions/about-text-annotation-format/m-p/835389

internal class ChangeSymbol : Button
  {
    protected async override void OnClick()
    {
      var annoLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<AnnotationLayer>().FirstOrDefault();
      
 
if (annoLayer == null)
        return;

      await QueuedTask.Run(() => {

        var select = annoLayer.GetSelection();
        if (select.GetObjectIDs().Count() > 0)
        {
          var oid = select.GetObjectIDs().First();
          QueryFilter qf = new QueryFilter()
          {
            WhereClause 
 
= $"OBJECTID = {oid}"
          };
          var rowCursor = annoLayer.GetTable().Search(qf, false);
          rowCursor.MoveNext();
          var annoFeature = rowCursor.Current as ArcGIS.Core.Data.Mapping.AnnotationFeature;
          var graphic = annoFeature.GetGraphic();
          var textGraphic = graphic as
 
 CIMTextGraphic;

          var op = new EditOperation();
          op.Name = "Change Anno";
          op.Callback((context) => {
            //make the callout for the circle
            var callOut = new CIMPointSymbolCallout();
            callOut.PointSymbol = new CIMPointSymbol();
            //Circle outline
            var circle_outline = SymbolFactory.Instance.ConstructMarker(40, "ESRI Default Marker") as CIMCharacterMarker;
            circle_outline.Size = 30;
            //eliminate the outline
            foreach (var layer in circle_outline.Symbol.SymbolLayers)
            {
              if (layer is CIMSolidStroke) {
                ((CIMSolidStroke) layer).Width = 0;
              }
            }

            //Circle fill
            var circle_fill = SymbolFactory.Instance.ConstructMarker(172, "ESRI Default Marker") as CIMCharacterMarker;
            circle_fill.Size = 30;
            //eliminate the outline, make sure the fill is white
            foreach (var layer in circle_fill.Symbol.SymbolLayers) {
              if (layer is CIMSolidFill) {
                ((CIMSolidFill)layer).Color = ColorFactory.Instance.WhiteRGB;
              }
              else if (layer is CIMSolidStroke)
              {
                ((CIMSolidStroke)layer).Width = 0;
              }
            }

            var calloutLayers = new List<CIMSymbolLayer>();
            calloutLayers.Add(circle_outline);
            calloutLayers.Add(circle_fill);
            //set the layers on the callout
            callOut.PointSymbol.SymbolLayers = calloutLayers.ToArray();

            //set the callout on the text symbol
            var textSym = textGraphic.Symbol.Symbol as CIMTextSymbol;
            textSym.Callout = callOut;
            textSym.Height = 8;//adjust as needed

            //now set the text
            textGraphic.Text = "12 <SUP><UND>00</UND></SUP>";
            annoFeature.SetGraphic(textGraphic);
            annoFeature.Store();
            context.Invalidate(annoFeature);
          }, annoLayer.GetTable());

          op.Execute();
        }
      });
    }
  }‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍