It may not technically be in the EULA but it's clearly not in the spirit of the license agreement. You can use a DLL to do any sort of modification of an executable (removing nag screens for instance) without having to actually touch the contents on disk, but that doesn mean it's "right".
I don't think changing the version reply is or should be supported here, frankly. If Khaled wanted people to change the reply he would not have put a fence up around the CTCP VERSION event. I think that settles the official sentiment on the issue, whether it's written in the EULA or not. Those who don't respect the authors wishes can feel free to write their own client free of all restrictions. Until then, the "version" of mIRC should always be "mIRC" and Khaled should get his credit where his credit is due.
Keep in mind that even in Open Source Software it's illegal to claim someone else's work as your own. It's called a copyright violation and needs no EULA to be enforced. Changing the version reply to say you're using "MY IRC SCRIPT" without mentioning mIRC would be doing just that.
