First, if i have posted in the wrong place i apologize, as i did not notice a more accurate place to post.
Anyhow
Converting a world's block IDs/item IDs is possible using a program called mIDas GOLD, but it's highly impractical to correctly input all the conversion values this program needs by hand especially when your using several mods.
But your in luck because mIDas GOLD v0.2.1 has a "patch" load function.
So i made a simple program called mIDas Patch Maker to utilize this function.
Basically, you provide the patch maker two copies of the same mods.cfg file.
The first copy containing the Block/Item ID's your world was generated with, should be renamed "old.cfg" and placed into the mIDas Patch Maker's directory.
The second copy should have correct/new Block or Item ID values you want your world to use. And should be named "new.cfg" and placed into the mIDas Patch Maker's directory.
With this information in place, run mIDas Patch Maker, and if all goes well, you'll have a new text file ready for mIDas GOLD named "Patch.txt"
For Download Links, pictures, and Full instructions visit my thread on Minecraft Forms Here
Legal:
I'm too dumb to use any sane license like the zlib license, the GPL, or the BSD license so a mod replaced the former "license" with this message. Hooray!