Can you downgrade from SQL Enterprise to SQL Standard?
Question: Can a TFS 2010 Team Project Collection (TPC) on SQL Server 2008 Enterprise be down converted to SQL Server Standard 2008 edition?
Answer: This is covered in the 2010 Upgrade guide post.
The script is: exec prc_EnablePrefixCompression @online = 0, @disable = 1
(answer provided by Ed Holloway)