This STSADM Command Extention was created for the purpose of repalce a value in the Membership URL with a new value.
For example: Reaplce 'bob with 'joe'
http://bob/page.aspx -> http://joe/page.aspx
http://server/bob/page.aspx -> http://server/joe/page.aspx
http://server/site/bob.aspx -> http://server/site/joe.aspx
It just does string matching