How to change the incoming xml to a different namespace

I have a xml file coming into XI (file ->XI)without namespace. I would like to change the root elment with ns tag add the namespace values with it.

ie.,

Coming in as

<Vendor>

.......

</Vendor>

I would like to change it to

<ns:Vendor xmlns:ns="urn:group01:legacy">

......

</ns:Vendor>

thanks