One thing you could do now to prep for that is to create a new profile that is not set to use the latest version, but to historic versions, and set it to 1.12. Never open your current world unless you know you are in that profile.
I don't think the updates are coming too fast, but I think that the developers are under a lot of pressure to produce new material, while simultaneously hounded by people who are bitter about various changes, like the anti-combat update crowd. They are being told "Add stuff, but don't change anything! And if you don't add stuff, it means Microsoft is abandoning the game! But if you do add stuff, it means the game is getting bloated (1)!"
Not a good position to be in.
First of all, I know how to change the version. The thing is, it's not fun playing Minecraft 1.12, when 1.13 will be out, since it will be more advanced and will have more features.
(1) Minecraft is the last game to be bloated! Minecraft is doing great, and is definitely not bloated. If you think it is bloated, then it is your problem, and you should go play another game. There are billions of players who enjoy Minecraft the way it is, so let it be. And hey, what do the ones who don't enjoy the 1.9 combat do? They play 1.8 PVP on 1.8 PVP server. In fact, I know only a few servers that use 1.9 PVP, so yeah.