Step 1.
Using the IMGtool open player.img in your models folder.
locate tshirtsuburb.txd back up orginal file then replace with file
in this zip folder. remember to rebuild archive and close.

Step 2.
Go to one of your safe houses. 
Go to the change room and scroll down to Sub Urban
Change the shirt your wearing to the Suburban T and that will be the zoo york t-shirt.

Step 3.
Enjoy