Unlink an existing copyed precomp

You can check out True Comp Duplicator. It duplicates all the precomps in that comp before you start to make your edits. But I don't think you can get your precomps back to the state before you've made the changes if you didn't make a save before hand. Sorry bud! Hope this helps!

You can try some of the scripts on AEScripts.com that offer mass substitution and relinking of assets. It may not get you there all the way, but it should at least facilitate soem of the process. Otherwise you can always try and manualyl replace your assets in each comp timeline with that Alt + drag&drop thing to "unlink" nested assets and replace them with independent ones.

Mylenium