How to temporary disable bookshelves

If you don't want to set up a Sticky Piston system to retract and extend the Bookshelves, you can place a torch or place water in the area where the Bookshelves are. For some reason, this disables all of the Bookshelves and makes the Enchanting Table act as if there aren't any Bookshelves around it.

The only way I can think of is through the use of sticky pistons that can push or pull some bookshelves out of the way. You can control the whole thing through a system of levers.

Keep in mind that only the 5x5x2 wall is checked, so pulling any shelves out of that area will "disable" them.

As Jake King suggested, you can use sticky pistons, and I've made a video to explain (made it before the first answer, but it was uploading too long).

It isn't that hard, you'll need a piston for every bookshelf, so it's 30 pieces. The tricky part is to get 30 slimeballs, but you can farm them. If you are okay to use an utility - you can find it here, but if you aren't - just explore some caves close to the bedrock and remember the place, where you have seen any slimes. They spawn in certain 16x16 chunks, so you'll have to dig out a big ~32x32 room somewhere between levels 10-40, they'll spawn there eventually. Good video tutorial and text tutorial.

UPD: I've upgraded my system. Nothing complicated, but it gives access to any enchantment level (not just the lowest and the highest). Still uses 30 pistons, but I'm an aesthete and I don't like how other solutions look/work.