A: Yes, but be careful. If your precomp contains cameras or lights, un-precomposing will break the 3D space. The script will warn you (or you have to manually re-enable 3D switches).
: Pulls all layers out of a pre-comp and places them directly into the root/parent composition timeline. Un Precompose After Effects Plugin Free Download
Go back to your main timeline and hit Ctrl+V . A: Yes, but be careful