There is no reason for you to be the boss of Hotrod. He is your feathered companion and he has his own likes and dislikes. He doesn't work for you! A relationship with a bird should be built on trust and understanding. Positive reinforcement training can be used to bridge the communication gap between us. Ya, sure, parrots can learn to parrot humans, or maybe even learn to talk, but we can't speak bird!
Positive reinforcement training (often under the guise of clicker training) is a means to learn how to communicate with animals in a positive manner. It's about learning how to understand their body language, learning when to back off and when to go forward.
If Hotrod is on your shoulder and you ask him to step off and he bites, he's telling you he doesn't want to come off. What reason does he have to come off when he's happy where he's at?
Well, here's where your training comes into place. You need to find out what Hotrod loves. What Hotrod will do anything for. Is it a favorite treat? A piece of food? A toy? Going somewhere? Is he willing to step up for that item?
You need to teach him that doing as you ask (not demand) brings positive rewards for him. The more you reward him for doing as you ask, the more he's likely to continue that behavior.
The best way to teach Hotrod to step up from your shoulder is to first teach him to step up from various locations. Once he's good at stepping up from one location, add in another location. Keep doing this until Hotrod steps up well from various locations and he gets rewarded for it each time. Then, you can try teaching him to step up from your shoulder.
Otherwise, you may want to prevent him from sitting on your shoulder, thus preventing him from biting you in that kind of situation.