If you did the code correctly, you'll here the dolphin squeak when you cross the finish line. If you reset and go the title screen, you'll see people riding on dolphins.
To ride a dolphin, select Championship Race, normal mode. Hold down on the analog stick when selecting your racer. In Dolphin Park, you will ride a dolphin.
The code is perminant and even after you turn off your N64 it will still be there. So you can
do it again and again.