I don't think you need to give antibiotics for fractures, so don't worry about that. Best way to remove feathers is to gently pluck them in the direction they are growing. Was the splinting manual helpful?
"The first step in splinting this cockatiel fracture is to remove all the feathers over the fracture site. Plucking them allows them to grow back faster compared to cutting them. You can see the bruising that is apparent on this birds leg directly over the fracture. Birds routinely show bruising...
When non-veterinary people, myself included, try splining fractures we often do more harm than good. From what I know, the joints above and below the fracture need to be immobilized. Attached is an avian splinting manual. @BantyChooks , any advice?
You can probably rule out blackhead, though I did hear about one case where the liver was clean. Coccidiosis can affect different parts of the intestines, which is why it's important to take a close look at them.