How Do I Prevent the Minecraft Launcher From Overwriting an Old Optifine Installation?

I am playing Minecraft 1.0.0, and I want to install Optifine. I found a legacy download for the 1.0.0 Optifine version, and installed it the way I did when I first played: open the .jar file in an archive editor, open the Optifine zip file, drag contents of Optifine into 1.0.jar, etc. Then, when I ran the game, Optifine was NOT installed. The launcher decided that I didn't know what I was doing and "fixed" the contents of 1.0.jar. All the solutions I found online referred to deleting a section of the 1.0.json file to prevent the game from validating the contents of the client. So, I did that, and lo and behold, the .json was ALSO "fixed" back to default. This is absolutely ridiculous, and after this, as well as the latest "Content Guidelines," there's no way that the game isn't hemorrhaging every pre-2016 player and content creator. There must be some way to install a simple performance mod that has existed since the game was in Alpha.

Also, this is a version that does NOT have an Optifine installer, because the installer wasn't necessary until all the ridiculous "validation" was added to the launchers. If it did, I wouldn't have this problem.

:)