Excellent guide, but PLEASE consider changing the reported difficulty to medium (iFixit, if that's not something the author can do). The process is actually super easy, but just takes over an hour to do.
I nearly didn't do it myself after realising it was rated the same difficulty as an SSD/HDD change in an iMac (with which I cracked my screen in two places), but it isn't. This is about a 2/10 difficulty level, and that's about 9/10.
I just think it would be a shame if the reported difficulty dissuaded people from doing it, and wasted hundreds of dollars paying Apple to do it. If you can read, and have the equivalent dexterity of tying shoelaces, you can do this. :)
Also, the battery removal is a pain, but if you cut an old credit card down the middle, you have two "spudgers" you can use underneath in a turning motion (sort of like rotating a lever in-plane), while pulling it in and out. A bit of patience and you'll get each half out in about 5 minutes.