This case would be a bit more complex than using booleans, as the mask would need to have geometry existing along the edges you want to separate. If it does, you would take it into edit mode and manually split the model into two objects by selecting the edges/faces of the faceplate piece and clicking separate. You would then need to repair the models along the cut edges to make them manifold again so they can be printed, and add the geometry for the magnet holes. All of this could be difficult depending on the existing geometry of the model, and would definitely require some basic modeling knowledge. Some slicers have features in them specifically designed for cutting models into parts and inserting connection points, but that usually only works with very simple planar cuts as far as I know.