But even if they were willing, it doesn't matter. Because the ugly truth is that, given its preferred coalition arrangements, National's "promises" are irrelevant.
Look at the current coalition. Elected without much of a plan, National signed coalition deals with ACT and NZ First which puts the latter two parties in the policy driving seat and lets them call the shots. And this is only going to get worse. All the polls show National will lose seats in the election, so even if the regime manages to retain power by election rigging, National will have less power in it than they do at present. Which means even more NZ First and ACT policy, and even less of National's.
In short, it doesn't matter what National promises this election. If they retain power, it'll be ACT and NZ First policy they're implementing. National's "promises" are simply irrelevant.