scala reflection - how to change (not only) private field

gistfile1.scala

  import scala.reflect.runtime.universe._
  import scala.reflect.ClassTag

  def setField[O: ClassTag, FV](obj: O, fieldName: String, fieldValue: FV)(implicit ev: TypeTag[O]): O = {
    import scala.reflect.api.JavaUniverse
    val ru: JavaUniverse = scala.reflect.runtime.universe //runtime universe
    val runtimeMirror: ru.type#Mirror = ru.runtimeMirror(obj.getClass.getClassLoader)
    val instanceMirror: ru.type#InstanceMirror = runtimeMirror.reflect(obj)
    val fieldTerm: ru.type#TermName = ru.newTermName(fieldName)
    val fieldSymbol: ru.type#TermSymbol = ru.typeOf[O].declaration(fieldTerm).asTerm.accessed.asTerm
    val fieldMirror: ru.type#FieldMirror = instanceMirror.reflectField(fieldSymbol)
    fieldMirror.set(fieldValue)
    obj
  }

  //usage
  case class X(i:Int, d:Double) {
    private val s = "I am private"
    def showMeS = s
  }

  val x =X(123, 0.001)
  assert(x.i == 123)
  assert(x.d == 0.001)
  assert(x.showMeS == "I am private")

  setField(x, "i", 103)
  assert(x.i == 103)
  setField(x, "d", 5.001)
  assert(x.d == 5.001)
  setField(x, "s", "Not any more...")
  assert(x.showMeS == "Not any more...")