This is in line with implementing the answer to Should we have a sub-tag for beta/RC?.
updating post history, 51 rows affected updating posts, 35 rows affected updating PostTags associations, 10 rows affected removing/renaming old tag, 1 rows affected updating count for master tag, 1 rows affected tag remapping of [windows-8-preview] and [windows-8] complete! remapping 0 synonyms 34 favorite and ignored tags remapped! Tag Synonym windows-8 -> windows-8-preview was approved!
Done. The synonym will be dropped later once Windows 8 is released.