Restart old world with a seed that no longer works?

[CozmicCadetz]

So, recently I was trying to gain access to an old world I had on my previous computer that had a pretty cool map (it spawned the lunar islands RIGHT NEXT to the mainland!) I first tried to get it through the world seed but learned very quickly the seed no longer worked due to the updates that happened between the creation of that world and me getting a new computer. I was able to get the save file off the computer and transfer it to my new computer but I was really hoping to be able to play the world from the start as it was originally made on the relaxed game mode and I want to play it on endless or survival.
I can do the normal reset method for worlds because when it resets it the map switches to the new map that now takes up that seed. I'm a little sad that I can't seem to get a clean version of the world anymore and was wondering if there was maybe another way to get the map that I just haven't figured out yet or if it is impossible and I'll just have deal with this save being the only version of this map/world I'll have.