title: Changing UITableView section header without tableView:titleForHeaderInSection
body: <p>I'm trying to change the header title for a section in a <code>UITableView</code> when a cell from that section is selected. <code>tableView:titleForHeaderInSection</code> is triggered by the application, so that doesn't help. I can call <code>reloadData</code>, but the performance suffers because the app has to reload all the visible cells. I also tried to use a custom header, but that also results in some performance problems. </p>
  
  <p>Is there any way to get a handle to the <code>UILabel</code> that the default header view uses and change its text manually? </p>