Minecraft: How can we repopulate a VANILLA world with MODDED ores?

Solution 1:

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.