Relax guys, and don't be mean to people who aren't super familiar with our rules.
A better way to credit FD or SB work that was created for an AU and is only slightly modified is to just do this:
(Original Artist, modified by Modifying Artist)
This is IMO the best way to describe how the original work was altered. It shows how the original artist does not necessarily condone the modification made of their work, which is an important stipulation in IP protection.