await QueuedTask.Run(() =>
{
//annoLayer is ~your~ Annotation layer...
// use the inspector methodology
//at 2.x - var insp = new Inspector(true);
var insp = new Inspector();
insp.Load(annoLayer, oid);
// get the annotation properties
AnnotationProperties annoProperties = insp.GetAnnotationProperties();
// set the attribute
annoProperties.TextString = "Hello World";
// assign the annotation proeprties back to the inspector
insp.SetAnnotationProperties(annoProperties);
//create and execute the edit operation
EditOperation op = new EditOperation();
op.Name = "Update annotation";
op.Modify(insp);
if (!op.IsEmpty)
{
var result = op.Execute(); //Execute and ExecuteAsync will return true if the operation was successful and false if not
}
});