Adjusting C# class attributes to produce right XML

Question

I have C# class with this header

[System.SerializableAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true, Namespace = "http://www.finacle.com/fixml")]
[System.Xml.Serialization.XmlRootAttribute(Namespace = "http://www.finacle.com/fixml", IsNullable = false)]
public partial class FIXML

which produces XML like this

 <?xml version="1.0" encoding="utf-16"?>
  <FIXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="https://www.finacle.com/fixml">

Problem is I need to have different header, with custom schemalocation and encoding.
Which attribute I can use to produce this output :

<?xml version="1.0" encoding="UTF-8"?>
<FIXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.finacle.com/fixml executeFinacleScript.xsd" xmlns="http://www.finacle.com/fixml" >