HTTP hearder rewrite

Have you looked at the HTTP::header commands? One way to accomplish what you want is with the 'replace' command. If you want to change the value of header Foo to 'efg123', you could do:

  
  when HTTP_REQUEST {  
       HTTP::header replace Foo efg123  
  }  
  

There's more on HTTP::header here:

http://devcentral.f5.com/wiki/default.aspx/iRules/HTTP__header.html