Yes the EULA prohibits me from modifying/reverse engineer the games files. However I am merely using something that someone else did, not modify them myself. Not that I have read any EULA to the last row bit I think that makes it allowed? Anyhow I can imagine that using cracks is kinda a grey area as its not directly prohibited by any EULA but it could be read in a way that makes it forbidden... Or something like that...
Also getting a new disc from the publisher will cost you some money in shipping. So why do that when I am allowed to make my own backups?