Gonna get worse than that before it’s done. If the plate tectonics stop it will mean that the earth’s core will be running out of fuel and the magnetosphere will fade. then the atmosphere will begin to be stripped away and radiation will give us all real bad sunburns.
We probably could use electron guns to fire electrons into space leaving the earth with a net positive charge, coupled with earth’s spin, this would generate a global magnetic field.
Of greater concern is the carbon cycle where all the dead marine life sink to the bottom of the ocean trapping the carbon there.
I guess we could do massive dredging to recover the carbon.
The electron guns might be placed on mars to generate a magnetic field and then you need to crash a mostly icy comet into mars to get the water back.