title: How to make changes to SKActions periodically?
body: <p>I want to change the speedOfRectangle after spawning a few rectangles(SKShapeNodes).</p>
  
  <pre><code>func wait(factor: CGFloat = 1) -&gt; SKAction {
      return SKAction.waitForDuration(NSTimeInterval(rectHeight * speedOfRectangle * distanceBetweenRectangles / factor))
  }
  
  let spawnSequence = SKAction.sequence([wait(), increaseCounter, spawnAction])
  let spawnSequenceForever = SKAction.repeatActionForever(spawnSequence)
  
  worldNode.runAction(spawnSequenceForever)
  </code></pre>
  
  <p>How to make changes to SKActions periodically?</p>