Question: I'm currently stuck in the process of trying to finalize a modded world in Minecraft. I need to repopulate ALREADY CREATED chunks with ores from mods.

For more context:

* We're trying to use a 1.7.10 **Earth** map. We found a couple, all of which look fine and okay.
* We're also trying to use a 1.7.10 modpack
that is personalized to fit our Minecraft experience. It includes
simpler mods like ArchimedesShips and Flans as well as
worldgen-spawning stuff like Thermal Foundation, IC2, Tinker's
Construct, and Pam's HarvestCraft

Particularly, the combination of the above premises is something I can't do, but are exactly what I need to do. I'm fairly familiar with MCEdit, MultiMC, COFHCore, WorldEdit, etc., so any combination of such to produce the modded ores would be the appreciated. The closest I've gotten to such a world was using COFHCore to regen ores which kinda did it. Through some config file tampering I got Thermal Foundation ores to generate in the Vanilla Earth map. However, two problems arose: ONLY thermal foundation ores were regen-ing into the vanilla map, and it simply took too long and by the time I checked in (2 hours into regening) on how much has regened, only a part of India got all the cool new ores. 

I know this might seem impossible, but I got close to what I was hoping for, so I know it's possible. I'm hoping that someone out there might know the answer or at least another step to finding it. This is a really cool idea and I would appreciate any help. Thank you.

*NOTE* All help is appreciated, but please don't ask me to delete chunks in MCEdit. I understand that I can delete chunks to get new chunks with modded stuff, but that's not what I'm looking for.

Answer: 
Assuming that, for example, the Earth map has nothing relevant below level 65 (or however far down you need to go). Start any old map with all the relevant mods and allow it to generate sufficient chunks so that it is the same size as your earth map.

Copy everything from the generated world at say, level 60 and lower and copy it into you earth map at level 60 and down. Replacing the vanilla generated ores with the modded ones.

Its a hell of a lot of work, so you might create a sort of grid system. Coping 10 by 10 chunk areas at a time and deleting them (or cut and paste) from the generated world as you go to help you line them up.

You might also start by deleting everything level 60 and below so you can see your progress.
I, off the top of my head, recommend selecting a large area of the modded ores in WorldEdit, going over to the already loaded chunks, and manually pasting the ores around everywhere. I'm sure there's a more efficient way of doing this, but this is probably the easiest way I can think of that doesn't require any other programs. The command would be something like

//pos1 ~1000 ~-255 ~1000
//pos2 ~-1000 ~255 ~-1000
//paste

**Make sure to paste it elsewhere, to avoid having a giant chunk of land in your world**

Select the pasted chunk

//replace (all blocks other than your special ores) air
//copy

Then go back to the terrain and paste your structure (which should be all ore veins) with

//paste -a

This will paste only the ores and not disturb anything around them. Not keeping the *-a* could paste all of the selected blocks, including air, and would thus create a massive cube of floating ore veins.

The only downside I can see with this method is there being floating ores inside caves. Not sure what to do there.

Good luck!