Is it possible to generate alpha worlds with specific seeds?

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 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'm nearly 6 years late, but someone made a fabric mod which adds a seed selector into alpha 1.2.2a. Here is a zip you can import into MultiMC to use fabric mods in 1.2.2a.