Phospholipid Bilayer structural reversal
This would have quite dramatic consequences. The layers are ordered in the way they are, because of their polarity. In the way they are ordered, the hydrophobic tails are inside and directed towards each other, the hydrophilic heads are orientated to the outside and inside. Since both sides of the membrane are surrounded by aqueous solutions, this is necessary to allow a contact between solution and cell membrane and to allow an exchange of molecules between them. If the layers would be oriented the other way, this contact and exchange wouldn't be possible. Proteins channels in the membrane wouldn't be possible as well, since the intermembrane domains are composed preferrably of amino acids with hydrophobic sidechains, while the domains on the outside of the membrane contain more hydrophilic amino acids.
A turn like this would need a completely different composition of life - meaning it couldn't be based on water like it is.