Question: I have some seeds from some old worlds I want to see again, is there a mod that allows the ability to create alpha worlds with seeds or would it be possible to make a world blank but with the seed so that when the world is loaded it generates the world with seed using the generation type of that version?

Answer: 
Here is how you can make a world with a custom seed in Minecraft Alpha, before you could change the seed in-game

1. Start Minecraft Alpha by changing the version in the Minecraft Launcher
2. Create any world, and save and exit Minecraft
3. Use [NBTedit](http://www.minecraftforum.net/topic/6661-nbtedit/) to open `level.dat` found in the `saves/` folder of `.minecraft`
4. Open `Data/RandomSeed` and change this to your seed you want
5. Delete all the chunk files
6. Open the world in Minecraft again
I found a mod that let's you use old alpha seeds if you're still looking for this. There's no need to do this whole world update stuff just download this mod for 1.12.2. I know it says it's a server plugin, but I can 100% guarantee that it will work like any other mod, just download forge for minecraft 1.12.2 and drag this mod into the mod folder, when you're creating a world, select "world type: alpha 1.1.2\_01" and then you're done. This mod doesn't generate villages or anything like that, but if you're using mods such as recurrent complex, rouge-like dungeons etc. it will generate those structures. Anyway Here's the link.

<https://forums.spongepowered.org/t/nostalgiagen-0-6-generate-minecraft-alpha-beta-worlds-on-your-sponge-forge-server/10126>