Access underlying base imagery with MkTileOverlay or MKTileOverlayRenderer?

Question

I am providing and rendering MapKit tiles in a usual way:

class TileOverlay: MKTileOverlay {
    override func url(forTilePath path: MKTileOverlayPath) -> URL {
        // Calculate URL for index path
        return url
    }
}  

public override func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer? {
    if let overlay = overlay as? TileOverlay {
        let renderer = OverlayRenderer(tileOverlay: overlay)
        return renderer
    }
    return nil
}

open class OverlayRenderer : MKTileOverlayRenderer {

    override open func draw(_ mapRect: MKMapRect, zoomScale: MKZoomScale, in context: CGContext) {
        UIGraphicsPushContext(context)
        super.draw(mapRect, zoomScale: zoomScale, in: context)
        UIGraphicsPopContext()
    }

    public override init(overlay: MKOverlay) {
        super.init(overlay: overlay)
        self.alpha = 0.5
        self.blendMode = .multiply
    }
}

That works fine, but I need to access Apple's underlying image for pre-processing before or when performing the MKTileOverlayRenderer draw function.

I have reviewed documentation and searched high and low for a way to access the base imagery but have yet to find a solution. So, I thought the best way to solve the issue was to request the imagery with MKMapSnapshotter and pre-tile it. However, it has been hinted that there is a way to access the underlying images, see:

Determine MapKit tiles for visibleMapRect