Change the size of an accessoryView on UITableViewCell

This can be done in the UITableView's cellForRowAt method:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
     let cell = tableView.dequeueReusableCell(withIdentifier: "customCellID", for: indexPath) as! CustomTableCell
     cell.accessoryView = UIImageView(image: "imageName")

     // This is where the magic happens
     cell.accessoryView?.bounds = CGRect(x: 0, y: 0, width: 50, height: 50)
     return cell
}