Kolasanic was being played as a CB when he first arrived. We didn't have a plan for him when he arrived. He caught Wenger's attention because he was available on a free.
I can't see us changing systems to accommodate whoever comes in. At best, we'll go back to playing 4-2-3-1 and he'll find a way to fuck that up. Wait until Ramsey is fully fit and Wenger tries to think of a way to play him, Wilshere, Xhaka and Ozil.