You can replace top part requiring only the bezel for the display but it's extremely delicate while adjusting display layers on it. Bottom panel and top case with keyboard is not a big deal that you can do with adequate ESD precautions otherwise your Unit will be totally exposed to immediate to future failure. The safety of the battery is also very important. If a unit is dropped, Apple suggests to replace the battery even if it's working. It's all up to users how they refrain to.