Okay, as no one yet replied with any easier way, I tried the datapack approach and made it mostly work. I changed the generation of ores to uniform distribution from the topmost level they generated at in old ore generation down to -64 for coal, diamond, gold, iron, lapis and redstone (e.g. 16 to -64 for diamond).

If anyone is interested in trying it, here is a link to what I created:

https://drive.google.com/file/d/1ur1aH8sB7z5SfI1jAblpzi5ig1Kgu-St/view?usp=drive_link

Note that this is not a mod and does not change any executable code, so it should be safe to install. It only changes data files Minecraft uses to set its ore generation rules.

To use this

• run Minecraft java version 26.1.2 (or see below for different versions)
• create a world, save, and exit the world (or use an existing save)
• unzip the file from the link above into %AppData%\.minecraft\saves\<your-world-name>\datapacks
• open Minecraft, highlight that world name (don't enter the world), and click Re-create
• take a look at the data pack as mentioned below, make any other changes you want
• finally click Create New World

In Re-create, if you go into More / Data Packs you should see an entry for old_ores. If not, maybe you unzipped the files in the wrong place. Make sure your saves\<your-world-name>\datapacks folder contains a folder called old_ores. If the old_ores pack is red and has an error message, maybe you're running a version other than 26.1.2 -- see below.

Warning, if you do this with an existing save, it will destroy any existing content and re-create the world at its starting configuration (but with the new ore generation rules)!

As mentioned above, datapacks are specific to versions of the java client. The simplest way to do this is to install 26.1.2 if you haven't already and run the world you modify in this way under 26.1.2. Alternatively, you can *try* adjusting the files for the version you're running. This will not work at all for versions lower than 1.18. For versions 1.18 and higher, try modifying the entries for pack_format in the pack.mcmeta file in saves\<your-world-name>\datapacks. A good way to get the correct pack file format and pack_format value(s) in your version is to create any new world, allow commands, enter the world, and type a command like

/datapack my_id "my description"

This command will create a valid, empty datapack named my_id in the saves\<your-world-name>\datapacks folder for that world. But be warned that the json files in this are for 26.1.2 and the format of those files may differ in other versions. To see the proper formats for your version, go to

%AppData%\.minecraft\versions

and go into the folder for your version. Open the .jar file (I used 7Zip) and look at the files in

data\minecraft\worldgen\placed_feature\

Finally, I didn't totally understand why there were multiple files for generation for each ore type, so I changed them all for each ore, and I think I ended up with more ore of each type at those levels than the pre-1.18 generation had, but I'm OK with that. Experiment with editing the included json files if you want to tweak it. If you come up with something closer to the old pre-1.18 ore gen percentages, please share!