The proper construct would be “libre de ne pas faire” (which might indeed become “libre de pas faire” in familiar settings).

I would indeed translate “Libre de ne pas faire comme on nous dit.” as “Free not to do as we’re told”, as in “I might choose to ignore what you tell me and do something else”, not as in “I might choose to do what you tell me to”.

From my understanding, there’s a difference between

Ceci est à ne pas faire (literally, This is to not do)

meaning this has to not be done (please don’t do it), and

Ceci n’est pas à faire (literally, This is not to do)

meaning this is not needed (but could eventually, if you really want).