If you will not be attempting to manipulate the results as TSQL XML then the simplest thing to do will be create a varchar with the string you wish to append then add the XML to it using a CAST statemnt to convert the XML to varchar.
declare @testXML as XML
declare @testPrefix as varchar(255)
set @testPrefix = ''
set @testXML = ' Mike Sanfrancisco John NY '
select @testPrefix
Select @testXML
select @testPrefix + CAST(@testXML as varchar(max))