An example of swapping the GridFieldConfig of a particular GridField in a ModelAdmin

ModifyModelAdminGridFieldConfig.php

<?php

class Example extends ModelAdmin
{
    private static $url_segment = 'Example';

    private static $menu_title = 'Example';

    private static $managed_models = [
        Site::class
    ];


    /**
     * @param null $id
     * @param null $fields
     *
     * @return Form
     */
    public function getEditForm($id = null, $fields = null)
    {
        /** @var Form $form */
        $form = parent::getEditForm($id, $fields);
        $fields = $form->Fields();

        foreach ($fields as $field) {
            if (!$field instanceof GridField) {
                continue;
            }

            /** @var GridField $field */
            if ($field->getName() === TestScraperResult::class) {
                $field->setConfig(GridFieldConfig_RecordViewer::create());
            }
        }

        return $form;
    }
}

SS4 equivalent:

    public function getEditForm($id = null, $fields = null)
    {
        /** @var Form $form */
        $form = parent::getEditForm($id, $fields);
        $fields = $form->Fields();
        foreach ($fields as $field) {
            if (!$field instanceof GridField) {
                continue;
            }

            /** @var GridField $field */
            if ($field->getName() === str_replace('\\', '-', VideoCategory::class)) {
                $config = $field->getConfig();
                
                $field->setConfig($config);
            }
        }
        return $form;
    }