I don't see how Tesla wins either way. If it's not a safety issue and they go with "prolonging the battery", then the implication is that the batteries aren't lasting as long as they should have, so they have to remove features in order to stretch out battery life. So they lose the battle either way. If they identified a safety issue that required a change in order to prevent fires, that safety issue should have been reported to NHTSA before they issued a fix, else there is no tracking of the issue and fix. NHTSA is pretty specific on that front: safety issues have to be reported within 5 days of discovery. There is no disclaimer for "unless you already fixed it". On the other hand, if it's nothing but "prolonging the battery", many will perceive that as an admission that their batteries were discovered to not last as long as they should. So it's not a good situation either way.
Mike