[Blue Only Please] ENBSeries DX9 Mod?

I recently learned that there is a graphics modification for all DX9 games called ENBSeries. I have seen others use it in WoW. (*1) I was wondering if such a mod is allowed, as it doesn't do anything to the game itself, but it does affect the graphics given that the game uses DX9. (*2)

1 - YouTube Video Showing Comparison Before/After:
http://www.youtube.com/watch?v=qvk1--J8Nq4
http://www.youtube.com/watch?v=V0ycqm491qg
2 - Link to the ENBSeries site:
http://boris-vorontsov.narod.ru/index_en.html

Is this allowed to be used with WoW? Thanks in advance.

P.S. : To all devs/tech. support working on a Sunday - I salute you. Your service is truly remarkable and I thank you all very much.

P.S.S. : Yes, this is a repost from the Tech. Support forum as I feel that I could probably get a faster response from this forum and therefore better customer service. Again, thank you to all who help answer this question. =]