The question, answered:
DECLARE @strIn [nvarchar](2008)
SET @strIn = 'xxx,yyy,zzz'
A SELECT query:
SELECT REPLACE(REPLACE(REPLACE(@strIn,',',''','''),'xxx''','''xxx'''),'''zzz','''zzz''') As [simple]
If I misunderstood, I wouldn't post this as an answer.
[simple]
~~~~~~~~~~~~~~~~~
'xxx','yyy','zzz'