The walls at MOSI haven't changed since the Shack was moved in pieces through the hole that was then glazed. The Shack was reassembled inside the building so the hole doesn't need to be that big to get it in or out.
What has changed since it went inside is the fact that the Highways Agency want to charge for the necessary road closure needed to get it out and the figure I've heard for that is £20 000 a day. With the Science Museum and Manchester council arguing over who is responsible for repairing the roof I rather think the Shack will stay where she is until the fate of MOSI's aviation hall is decided.