A few years a go when I repaired condos intercoms many magnets left over from damaged speakers so I used them inside CD players trafos and as CD clamp, also in top of amps trafos, they were Ferrite donuts not Neo.
Place an magnet outside over the cabinet cover will no make much difference due the cover metal shielding, try inside direct over the Toroidal, use donut shape in the center.
Toroidals with strong shieldings will have small effect YMMV.