The Problem:-

How to rename a manually recorded file in media center?

Resolution:-

Locate the recorded program,it should be under C:\Documents and Settings\All Users\Documents\Recorded TV
Now right click on the recorded file and select rename.But the renamed file won’t show the changes when you will open MCE.To do that you have to edit the metadata using MetaDataEdit.exe as the information of the recorded program is stored  in metadata embeded in the DVR-MS file.

Check it here:-
Edit DVR-MS Metadata
http://blogs.msdn.com/toub/archive/2005/05/12/416874.aspx