add custom SAMLIdentifiers to SAML2:Assertion tag: xmlns:xs=""

Im using c# and the low level API and initalizing SAMLAssertion samlAssertion = new SAMLAssertion();

How do I add a custom value such as xmlns:xs=“<a href=“””>" into the samlAssertion node

so it looks like this

<saml2:Assertion xmlns:xs=“<a href=“””>" xmlns:saml2=“urn:oasis:names:tc:SAML:2.0:assertion” Version=“2.0” ID=“pfx20d4808a-5943-66af-8546-eb259e5a2c14” IssueInstant=“2017-12-17T20:53:12.743Z”>

You would need to convert the SAML assertion to XML.
For example:
XmlElement samlAssertionElement = samlAssertion.ToXml();
You can then manipulate the XML as required.
However, you shouldn’t have to alter the namespace prefixes.
All that matters are the element names and namespaces.
We use saml rather than saml2 for the prefix but anything can be used.
You can also add the XML schema namespace declaration if you like.