I show this in my platform tutorial (going in a tunnel and coming out) but basically like this.
Variables:
isShop = 0
playerX =0
playerY = 0
Just before the event to change to the shop layout set:
isShop = 1
playerX = Player.X
playerY = Player.Y (Player is whatever the name of your player object is).
Then on start of layout for the main layout create a sub event:
If isShop = 1
Set Player Position = playerX and playerY
Set isShop = 0
Something like that :). Then you a have that sub event for other changes that take effect after leaving the shop.