FeedMe Change Slug when Importing
I've managed to get it working with great help from Brad Bell and Oli.
The following code changes feedme slugs on Import.
use craft\feedme\events\ElementEvent;
use craft\helpers\ElementHelper;
use craft\elements\Entry;

Adding the following Event with the namespaces above works nicely.
        Event::on(
          Process::class,
          Process::EVENT_STEP_BEFORE_ELEMENT_SAVE,
          function(craft\feedme\events\FeedProcessEvent $event) {
            switch($event-&gt;feed['name']){
                case 'merchants':
                    $element = $event-&gt;element;
                    $element-&gt;slug = ElementHelper::createSlug($element-&gt;title.' '.'Whatever you'd like appended!');
                    break;
            }
        });