Is there any elegant way to execute specific code depending on the caller, using reflection or otherwise?

public string UserDefinedField
{
    get { return _userDefinedField; }
    internal set { _userDefinedField = value; }
    set { _userDefinedField = value; ChangedFields.Add(Fields.UserDefinedField); }
}

public string UserDefinedField
{
    get { return _userDefinedField; }
    set { SetField(value); ChangedFields.Add(Fields.UserDefinedField); }
}

// Call this from internal methods and use the public property for other cases
internal string SetField(string userValue)
{
    _userDefinedField = userValue;
}

public string UserDefinedField
{
    get { return InternalUserDefinedField; }
    set { InternalUserDefinedField = value; ChangedFields.Add(Fields.UserDefinedField); }
}

internal string InternalUserDefinedField
{
    get { return _userDefinedField; }
    set { _userDefinedField= value;  }
}

...
internal void SetUserDefinedField(string val) {
  _userDefinedField = val;
}
...

// assumes callers know where they're located at in the current stack trace.
private Boolean IsExternallyCalled(int methodDepth)
{
    System.Diagnostics.StackTrace trace = new System.Diagnostics.StackTrace();

    System.Type callingType = trace.GetFrame(methodDepth).GetMethod().ReflectedType;
    System.Reflection.Assembly a = System.Reflection.Assembly.GetAssembly(callingType);

    return !(a.Equals(System.Reflection.Assembly.GetCallingAssembly()));
}