Regenerate Minecraft + Modpack + Chunks?

We have a server with 200h game time and our buildings arranged randomly in a four corner of 500 blocks. We just started working on creating the world, but now we would like to restart under the world type Biomes O Plenty. Is it possible to leave said square as it is and to have all other chunks regenerated with the new world type?

If you take the mod purely all the chunks that have not yet been loaded, so be regenerated with the mod loaded, it would be so far as I know at most possible with a command your settlement far away to copy, but this will make problems s.den edges, especially in terms of height and it would be a lot of work to terraform that it looks natural

Edit: but I could be completely wrong

Take World Edit. Mark everything and save as schematic. Create new world, load and paste schematic.

For 500 * 500 blocks you should not do that as a copy. Better to use smaller sections then works even easier insertion.

Whether World Edit, however, comes with all Modblöcken clear I can't promise you. Especially cables could cause problems.

And do not delete the old world beforehand if something goes wrong.