I found YAF and found it is a good fit for me.

I would like to customize YAF, before doing that I want to make sure there is no license issue for customizing it.

I'll keep the footer "YetAnotherForum.NET Copyright © 2009 Tiny Gecko.", plus I'll add something like "Powered by YetAnotherForum.NET" at the top of my forum pages. Other than that I am going to change lots of things so the forum may end up quite different from the YAF look-an-feel.

Is there any license issue for doing that kind of customization?