I'm familiar with the magneto shield, but I think it has huge problems. The counter weight is good, but natural objects in Lagrange Points still bounce around a lot. Give that disk a good size CME and see what happens. And the energy required is huge, I don't think solar power is up to the job. Furthermore, the sun/mars L1 is too far away, in my opinion. Mars sits in the tail of the magnetic shield, not in the middle.

Even with the hole in the middle, sunlight gets diminished by shading or diffraction. A hole is a lens. So now you have to build space mirrors to add light to the planet.

Over compensating for loss is just turning up the faucet on the bathtub with the open drain - still a huge waste of resource. Two steps up, one step down.

As far as the the amount of material currently being stripped from planetary atmospheres, I saw a paper recently about that. If I find it, I'll post it. Lack of data from other planets challenges conclusions.

As far as activating the core, well... First you've got to drill down that far, on an inhospitable planet. Second, earth magnetic dynamo is created in the outer core. It's the frictional effects of the inner core and the mantle that keeps the outer core dynamo moving. The heat comes from radioactive decay in the inner core. You'd have to keep dropping nukes down an impossible hole forever to keep it going. And how do you get that balance of solid inner / fluid outer core maintained?

(Edit-the glitch happened on this comment)