The magnets should be movable to the converted figure, but as the name of the figure has probably changed, you'll need to fix up that information in the base prop for each magnet (I think this mostly affects the parenting, as the groups should be the same).

The real problem is the need to reposition them and adjust the zones appropriately so that the vertices of the converted item that are affected match those affected in the oringal item, which is not likely to be a simple job, but ate least you don't have to start from scratch (assuming you manage to transfer the magnets in the first place).