I actually have the same request for a different reason. I'm running into an odd error myself with Pam's Harvestcraft, which I felt I might be able to fix if I can temporarily change one of the item ID numbers. But oddly enough, I don't see the numbers listed in the config to change.
I narrowed the problem down to the immature cinnamon block from the cinnamon tree in Pam's Harvestcraft. Holding that block is actually okay, but if I try to put the block down in the world, or I let the tree grow then attempt to harvest said block, it crashes my game. Tnere's also a error difference: putting the block down crashes it, but you can atleast recover the game. Harvesting it crashes it to the point you cannot recover your game...and that's the problem. I can't recover the game I'm playing. That's why I'm hoping if I change that number for a short time, I can hopefully stop the error in my game and bring it back. If that works, then I can switch the item number back, afterwards. Atleast that's my plan.
I did a data dump and found the item IDs, but I don't think changing it in a dump will change the ID number. So, I'm asking the same thing Eureka is....where are the item IDs for the mods now, and how do you change them?
I figured something had to change in 1.7.10, since they were all neatly listed in the dump without one space open in between. I found that very odd.