How to get the rename tool to work if it doesn't work for you
Solution 1: Make sure you have your mw2 called iw4mp.exe, check this by opening up task manager and going to processes and look for iw4mp.exe.
Solution 2: Make sure you aren't using the mod by an iwd or have any z_svr files around your mw2 folder because it stops it from working for some reason.
Solution 3: It could be the mod your using. A working mod with this rename tool is RSE v10. Mods that have bots that just walk around in circles don't rename for some reason.
Solution 4: Make sure your 4D1 files is in the same folder as to where your mw2 is installed, if it isn't go over to 4D1 and download the dedicated server update tool and stick it in your mw2 folder and run it.