How to add attributes like this to an XML node: mq:nodename=""

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C#

XML

I need to export a modified xliff file from my c# tool, but during the modification a different pre-tag is used instead the one I wish to use:
What i wish to appear is:
mq:status=""
What i get:
p8:status=""

I tried to read after this, and now I know that the pre-tags somehow relate to namespaces, but dunno how I can change it or add the "pre-tag" I want.

What I have tried:

This is the code which should change the file's content:

XDocument doc = XDocument.Load(filePath);
            XElement xliff = (XElement)doc.FirstNode;
            XNamespace ns = xliff.Name.Namespace;

            var testid = xliff.Descendants(ns + "trans-unit");

            foreach (var item in testid)
            {
                var iD = Convert.ToInt16(item.FirstAttribute.Value) - 1;
                item.SetAttributeValue(ns + "status", units[iD].Status);
                item.SetAttributeValue(ns + "locked", units[iD].isLocked);
            }

            doc.Save(destination + "\\EXPORT.mqxliff");