First post updated!
I've updated the tutorial so it won't break the promo code feature, and it will work with any mod that will require the edit of adopt.php and doadopt.php such as HoF's gender ratio system.
EDIT: Updated again! I added a security fix to prevent the user from using the GET method to enter any ID of an adoptables (with the condition of whenisavail set to always) and fill in the promocode with random string to bypass the security..Hopefully this will be the last problem I found with this mod