My tablet froze right in the middle of me finishing my above post...
I was going to say that if your Green Cheek is currently molting it will cause discomfort due to all the pin-feathers, but unless his change in behavior towards you started right as the molt started, then I doubt it's the reason behind his behavior change towards you (as all of mine are, my house has feathers floating EVERYWHERE right now, and they all have pin-feathers all over them and they're all miserable and constantly preening themselves and each other)...However, it will help him if you try either giving him a daily bath, shower, or misting with a spray-bottle, whatever it is that your bird likes as far as bathing goes, as it will help a lot with his itching. This can make them very grumpy, but it typically doesn't cause the behavior change towards their "person" like you're describing. But you never know...If his behavior changes back to normal after he's done molting, then you'll know that's what it was about...
The best thing you can do is to think back to exactly the time when his behavior towards you changed, and then think about ANY changes to ANYTHING that took place right at the same time that his behavior towards you changed...Any changes to your home, like any new furniture or other items in your home, any new people or animals, any less people or animals, any changes to his cage or what is inside of his cage or what's around his cage or to any of his perches/stands/gyms, any new toys or toys you took away, any changes to his food, any changes to his regular daily routine/schedule...If you started working a different job or shift, if you started spending less time at home or with him, any changes to your haircut or hair-color, any new scents on you or in your home, etc. The smallest, tiniest, insignificant little things that we would never think anything of can cause them great stress, even something as small as changing the soap you use, the laundry detergent you wash your clothes in, the perfume or cologne you wear, a different color of nail polish or hair color, cutting your hair suddenly much shorter than it was, etc. These are all examples of things that commonly cause issues with parrots and their people...
Also, if you relocated his cage in your home, or you moved something new next to his cage, or if you changed anything inside of his cage, this can cause great stress to them...You mentioned that he stopped coming out of his cage as soon as you open the door, he's doing it on his own time and not until you step away from his cage...That actually isn't uncommon at all, they are very territorial over their cages, and even the tamest, most loving, cuddlebugs still will not let their owners hands inside of their cages, even after years of being closely bonded to them...I have a Quaker Parrot that is turning 4 this year, I've had her since she was 12 weeks old and she's the sweetest, most loving parrot in the world, I can handle her any way I want to, she flies to me on-command, and she's just the most loving bird in the world...But I have to open up her cage doors and step away from her cage, and she'll come right out on her own and then fly to me and everything is great..If I open up her cage and put my hand inside to either remove her food/water dishes or to ask her to step-up and come out, forget about it, I'm getting a "warning nip" first, and if I don't remove my hand after that then I'm getting a good bite...So I have to actually have her come out on her own before I change her food/water...Otherwise she's fine with me doing anything I want to her, I clip her toenails and file them, I file her beak, she takes showers with me, etc., but my hands do not belong in her cage...So your bird starting that behavior is perfectly normal and may not have anything to do with the other changes in his behavior to you, like suddenly not stepping-up for you. If your Green Cheek is refusing to step-up for you while inside of his cage only, or is biting at you while inside of his cage only, but is still stepping-up while outside of his cage, then that's totally normal, and it probably won't ever change back, no matter what you do. You just need to respect his territory, and just open up his cage and step away and allow him to come out on his own, and THEN ask him to step-up, and THEN take his food/water dishes out and clean his cage. Don't try to have your hands inside of his cage at any time while he's inside of it, because you're not going to break him of this, and if you try you'll likely just cause more and more damage to your relationship with him...