XML : Modifiy SOAP header

Hello,

I need a to modify the soap header in order to add a specific parameter. After the tag " " i should be adding the parameter " soap:mustUnderstand="1" " but the data contained in the tag should not be modified.

The soap envelope is like this :

   
      
   
   
      [DATA]
   

Then soap envelope should like this :

   
      
   
   
      [DATA]
   

I know that i need to use the function stream in order to make it work but i need guidance on this one.

What should i put in the iRule in order to just add this parameter ?

Thank you for your help