Any mod that disables the pacification ?

Have you even completed Old World Blues yet? Probably not if you're looking for a mod to disable the pacification field so you can take out the Think Tank right away. Try playing through the DLC first before asking for such a mod.

If you have completed OWB before, killing the Think Tank early would essentially break the main quest-line of the DLC.

Like I said, it's an urge, not an informed decision. I'm deducing from what you're saying that I can kill them at the end of the DLC, yay !