This tiny LiveWhale application module limits the length of the summary to 90 words.

public.application.short_summary.php

<?php
 
$_LW->REGISTERED_APPS['short_summary']=array(
	'title'=>'Short Summary',
	'handlers'=>array('onWidgetFormat'),
);
 
class LiveWhaleApplicationShortSummary {
 
  public function onWidgetFormat($type, $handler, $variables) { // alter widget variables
    global $_LW;
    if ($type === 'news' && $handler === 'onDisplay' && !empty($variables['summary'])) { // find news widgets
      $variables['short_summary'] = preg_replace('~\.*\s*</p>[^<]*<p>\s*(\.\.\.</p>)\s*$~imsU', '$1', $_LW->setFormatSummarize($variables['summary'], 90)); // set short summary
      // unset($variables['summary']); // uncomment this to remove the summary
    }
    return $variables; // and return the variables
  }
 
}
 
?>

public.application.summary.php

<?php
 
$_LW->REGISTERED_APPS['summary']=array(
	'title'=>'Summary',
	'handlers'=>array('onWidgetFormat'),
);
 
class LiveWhaleApplicationSummary {
 
  public function onWidgetFormat($type, $handler, $variables) { // alter widget variables
    global $_LW;
    if ($type === 'news' && $handler === 'onDisplay' && !empty($variables['summary'])) { // find news widgets
      $variables['summary'] = preg_replace('~\.*\s*</p>[^<]*<p>\s*(\.\.\.</p>)\s*$~imsU', '$1', $_LW->setFormatSummarize($variables['summary'], 90)); // set short summary
    }
    return $variables; // and return the variables
  }
 
}
 
?>

Use one of the two example modules above or mix and match to meet your needs.

Short Summary it additive when the summary is present in the results. (The summary format variable is not always included, but you can change that by adding it to the default widget format.) Uncomment the unset to remove the summary otherwise.

Summary replaces the summary from the get go.