By default means of method, it is not possible to downgrade any save / nbt files from 1.3.0+ to 1.2.2- because MC official rewrote the NBT data structure. I think that is the reason why MCEdit is perma-broken too.
It is possible to be batch-edited in JSON format with a mod called NBT Explorer (https://github.com/jaquadro/NBTExplorer) to manually convert new block data to old ones, but it requires some work.
There might be mods somewhere which is technically very possible to revert nbt format, but I haven't found one myself. The last peroid I played MC was about 5 years ago and I updated things recently without such a warning before I realized people called that 'the update that destroys the world'.
Sorry for what I can't help. If you play from 1.3.0+, everything will be fine.
on January 6th, 2020 11:40 PM EST