Restarting the core not going to happen. But there's a "cheat code" - L1.

Put any human activity there, and you disrupt the solar protons eroding the Martian atmosphere and irradiating the surface.

Even the tiniest deflection is enough to make those protons miss Mars. NASA has talked about parking superconducting magnets there, but actually any human activity will do.

Using electricity? You're inducing magnetic fields. Industrial processes? You're leaking pollution. Transport activities? You're spraying propellant around.