Here is a utility I wrote a while back for changing more than one file names at a time in a single folder. It's a very useful tool and I use it from time to time when I need to change part of the file for more than a single file.
You can use it as you like. You can download both source and binaries.
System Requirements: x86, .NET 1.x or above, Window OS
Binaries - Bulk File Name Editor Binaries.zip
Source - Bulk File Name Editor Source.zip
Disclaimer: The software provided is as-is. Use it at your own risk. You are free to modify the code as you like.