emp:
Jupiter already has a very large and very powerful magnetic field: adding iron would probably not significantly improve it, as it is primarily due, if I remember the models correctly, to metallic hydrogen. And how would extra magnetism improve the chances for fusion? Fusion is driven by high temperatures and pressures driving more and more energetic collisions, which cause some fusion which releases neutrons which leads to self sustaining fusion reactions. Jupiter just does not have enough mass to do this.

"Enriching" the fuel would not help. If you have a drop of gas in your tank, it doesn't matter what the octane is: car will not go. Not enough fuel, not a matter of quality.