Hello Maniac00x,
To change the track it is the L3 button on PS4. R3 is for taking screenshots on PS4. And easily,it isn't hard to press and release the L3 while racing. I can change the track by holding the L3 button while racing. It isn't hard to do,I do it all the time. But having to hold it down to change the track is unnecessary when a simple press and release would suffice. Not to mention much easier to do while racing. I also mention changing it from the L3 button to the left and right d-pad buttons. Using those we could skip forward or back.
Wolf_Fangs1381