It is very simple to do and can be done in many ways.
You can have a variable called "character" and make that each character have it's own number so 0 is a duck, 1 is a cow etc. So when you drag the character of your choice into the center of the screen you set the variable to that number.
So on start of layout check the variable "character" and spawn the character with that variable number.
Hard to explain but very very easy to do