"After attacking" refers to a specific timing window, so it's pretty safe. "After Kozil attacks" is obviously the same meaning in a plain reading, but one could argue that by avoiding the classic construction we create some ambiguity. As such, you could mimic it a bit more by going with:
After attacking a small or medium figure with Kozil, if he rolled at least 1 skull and is still adjacent to that figure,
From a technical perspective it's still not
quite the same as the traditional "after attacking" window, because that window occurs even if you didn't attack, while this window obviously depends on an attack (a specific sort of attack at that) having happened. Still, mimicking the wording this way makes it pretty hard to misunderstand the timing.