My world is suffering from several chunk resets, probably due to ChicnkenBones chunk loaders (I'll migrate to railcraft's as soon as I fix this). After the first loss, I made a batch to backup everything every so often. And now I need to use them. I was able to open both current and backup in mcedit, find the reset chunk in each, but I don't know how to copy that individual chunk to another world…
What i tried:
I tried selecting it, opening chunck Options menu options, extracting it to a file (it created a folder with a single file there, the single chunk I tried to export), and then open the new world, select the same chunk and hitting import in the main menu; but it gives an error:
I don't know how to import this file: c.-k.k.dat.
Error: IOError('Cannot detect file type.',)
The error even makes sense, because I extracted in one menu and tried to import in another menu, that probably mean different things! But in the Chunk Options menu there is no import, and also, there is no export/extract in the main menu.
Picture of error: 
More info
I play on FTB, with Direwolf20 1.6.4 pack.
I am open to other suggestions if MCEdit doesn't work, but that seems to be the most important and common usage of such a program, I can't belived there is no way to do it.
I am considering the main menu to be the horizontal icon list at the bottom, that have the options: Select, Brush, Clone, etc., and the chunck control the vertical text list at the left that is open when you select Chunck Control (last option) on the main menu.
MCEdit version: 0.1.7.1.
Best Answer
I figured it out. When you block select something, there is an option select chuncks. So I just selected a few blocks on each chunck, hit Select Chuncks, and then exported. When you import, there is another crucial option Align chuncks, that will make placing it correctly very easy.