What is this?

[SO•Audiojack]

You could just try it ingame or in LFSViewer to see what has changed.

Here's also a nifty extension to Windows Explorer which lets you preview the actual texture in your folder
http://www.nvidia.com/object/dds_thumbnail_viewer.html
(install at your own risk, I use this extension but I know it can potentially cause explorer.exe to occasionally crash while browsing folders with a lot of .dds files in them)

Remember to ALWAYS BACK YOUR GAME UP when you change files so that you can revert in case you don't like it or the changed files produce errors or cause significantly lower performance.