Wordpress - Plugin upgrading: Widget settings

I've did a quick test on just changing the option and it seems to work.

What I did is:

1. Wrote a widget that has just 2 fields: "Title" and "Name". Add several instances of this widget to my sidebars. Been sure that they are shown correctly in frontend.
2. Edited the class to use 3 fields: "Title" and "First Name" (to replace "Name") and added "Last Name".

3. Edited the function that register the widget on 'widgets_init' to call a function that update the widget options:

   add_action( 'widgets_init', 'my_example_widget_register' );
   
   function my_example_widget_register() {
   
     $widget_name = 'my_example_widget';  // <-- You will probably replace this
   
     $options = get_option("widget_{$widget_name}");
   
     // if the widget is not updated, run a function that updates it
     if ($options && ! get_option("is_{$widget_name}_updated")) {
         // use class below to update options
         $updater = new MyExampleWidgetUpdater($widget_name, $options);
         $updater->update();
     }
   
     register_widget('My_Example_Widget'); // <-- You will probably replace this
   }
   

4. Wrote a simple class to update widget options:

   class MyExampleWidgetUpdater
   {
   
     private $name;
     private $options;
   
     public function __construct($name, $options) {
        $this->name = $name;
        $this->options = $options;
     }
   
     public function update() {
       // loop all the options
       array_walk($this->options, function(&$option, $key) {
           if (is_array($option) && is_numeric($key)) {
             $option = $this->getOption($option);
           }
       });
       // update all options in DB
       update_option("widget_{$this->name}", $this->options);
       // set the widget as updated
       update_option("is_{$this->name}_updated", 1);
     }
   
     private function getOption($options) {
       if (!isset($options['name'])) {
          return $options;
       }
       $options['first_name'] = $options['name'];
       $options['last_name'] = '';
       unset($options['name']);
       return $options;
     }
   }
   

5. I edited the widget class to save the option "is_{$widget_name}_updated" inside the update() method, in this way the updater class will never be called for new users that never installed old widget

   class My_Example_Widget {
   
       ...
   
       public function update($new_instance, $old_instance) {
           ...
   
           $widget_name = 'my_example_widget';
           update_option("is_{$widget_name}_updated", 1);
       }
   }
   

6. I visited my site and the widgets saved with old options are displayed with no issue using new options. (Of course "last name" is always empty).

A good idea may be replace the "is_{$widget_name}_updated" option, with an option that store the actual version of the widget, in this way it will be handy next time you need an update.