How to add a pane to a node with panelizer programmatically

custom_pane_panelizer.php

<?php
    // This code can be used in a hook_update_n to add a custom pane to an existing display in panelizer.
  
    // Example variables used in the code below.
    $nid = 1;
    $pane_machine_name = 'my_example_custom_pane';
    $region = 'content';
    $position = 0;
    
    
    // Load the node and save its display as modified, this is required so panelizer knows there's new stuff.
    $node = node_load($nid);
    $node->panelizer['page_manager']->display_is_modified = TRUE;
    node_save($node);
    // Change the display.
    $display = panels_load_display($node->panelizer['page_manager']->display->did);
    $new_pane = panels_new_pane($pane_machine_name, $pane_machine_name, TRUE);
    $new_pane->panel = $region;
    $new_pane->position = $position;
    $display->panels['main-content'][] = $new_pane->pid;
    $display->content[$new_pane->pid] = $new_pane;
    panels_save_display($display);

Relevant URLs:

https://www.previousnext.com.au/blog/updating-panelizer-content-programmatically
http://www.ygerasimov.com/panels-panelizer-snippets