Three dimensional ferromagnet-superconductor core-shell structures are realized by electrocrystallisation and their magnetic properties investigated. We observe fully re-entrant core superconductivity in increasing fields that survives well above the bulk critical field due to compensation effects. The net measured magnetization of optimized structures could be switched from absolute para(ferro-)magnetic to diamagnetic by tuning the external magnetic field. Micromagnetic simulations of the structures are in good qualitative agreement with our results.