This script takes selected rows in OmniOutliner, and tries to split topics that have multiple lines into multiple rows, and leaves one-liner items alone.

OmniOutliner-SplitRowsInTopics.js

// Based on information provided on
// https://omni-automation.com/omnioutliner/item.html

// Get selected nodes in foremost window (editors[0])
var nodes = document.editors[0].selectedNodes

// Split all selected topics in paragraphs
nodes.forEach(
  function(node) {
    // for each individual node
    var selectedItem = node.object
    
    // we get the parent so that we keep the relationship
    var selectedItemParent = selectedItem.parent
    
    // item.topic contains the outliner's text
    var selectedTopics = selectedItem.topic
    
    // split the topic in multiple lines per \n character
    var splitTopics = selectedTopics.split("\n")
    
    // for topics with more than one entry after splitting
    if (splitTopics.length > 1) {
      splitTopics.forEach(
        function(theTopic) {
          selectedItemParent.addChild(
            selectedItem.before,
            function(item) {
              item.topic = theTopic
            }
          )
        }
      )
    
      // we remove the item after having added the split topics
      selectedItem.remove()
    }
  }
)