Camry HO alternator question

I've never heard of such a thing. Not sure why you would ever do that. You really CAN'T bypass the ECM unless you are going a full stand alone harness with an aftermarket computer. Your engine's electrical components: (injectors, sensors), wouldn't know what to do.

Bypassing the ECM/PCM would be like taking the sheet of instructions for all your cars functions; headlights, injectors, door chimes, horn, lights.... anything that goes through the ECM/PCM then replacing those instructions with a blank sheet of paper.

I don't know about your specific vehicle, but I HIGHLY DOUBT THAT... A cheap HO alt will increase the pulley size to get higher amps... Any even semi-decent alt company will keep the same size pulley so that it will just be a simple swap. Any description about the alternator should tell if you will need to change the belt, or you can always contact the company. If you did need to change the belt, for a HO alt, they would increase the pulley size making it so you would need a LONGER belt. So that right there makes me think your friend doesn't know what they are talking about. The only reason you would need a shorter belt is when you use a smaller/underdrive pulley. People replace those with smaller pulleys to reduce the drag on the belt, making it seem as if your car is faster. When you do that though you are decreasing your Alternators output in exchange for less parasitic drag/faster "butt dyno" feeling.