XmlSerializer property converter

Treat the node as a custom type:

[XmlRoot("ObjectSummary")]
public class Summary
{
    public string Name {get;set;}
    public BoolYN IsValid {get;set;}
}

Then implement IXmlSerializable on the custom type:

public class BoolYN : IXmlSerializable
{
    public bool Value { get; set }

    #region IXmlSerializable members

    public System.Xml.Schema.XmlSchema GetSchema() {
        return null;
    }

    public void ReadXml(System.Xml.XmlReader reader) {
        string str = reader.ReadString();
        reader.ReadEndElement();

        switch (str) {
            case "Y":
                this.Value = true;
                break;
            case "N":
                this.Value = false;
                break;
        }
    }

    public void WriteXml(System.Xml.XmlWriter writer) {
        string str = this.Value ? "Y" : "N";

        writer.WriteString(str);
        writer.WriteEndElement();
    }

    #endregion
}

You can even make that custom class a struct instead, and provide implicit conversions between it and bool to make it even more "transparent".

The way I do it - which is suboptimal but have not found a better way - is to define two properties:

[XmlRoot("ObjectSummary")]
public class Summary
{
     public string Name {get;set;}
     [XmlIgnore]
     public bool IsValid {get;set;}
     [XmlElement("IsValid")]
     public string IsValidXml {get{ ...};set{...};}

}

Replace ... with the simple code to read and write the IsValid value to Y and N and read from it.