I love it when I can provide an answer! Assuming you have NEI installed, press E to open your inventory, then click Options button at bottom left of your screen. Click Tools, then click Data Dumps. On the line that says "Biomes" click the Dump button. Now go outside of Minecraft and navigate to your FTB installation folder, go into the modpack folder that you're playing, click on Minecraft and look for the Dumps folder. In that folder will be a spreadsheet listing all the biomes with IDs. When you first open the spreadsheet up (I use the free OpenOffice app for all my Excel/Word stuff now), you probably will get a popup - under "Separated By" (or whatever it might say), choose "Comma" then click OK.
Before you do the actual Dump of the spreadsheet, you can choose three options - "Used", "Free" or "All" as to which Biomes the Data Dump spreadsheet will list for you. It's the button just to the left of the Dump button. Given your issue, you may wish to experiment with that button and try all three.
That should do it for ya, good luck! I can't help you with changing the actual Biomes ID's within the game, but at least I got ya this far with it. You can prob take it from there.