add_action('product_designer_editor', 'product_designer_editor_20200808', 0);

function product_designer_editor_20200808($atts){


    $settings = isset($atts['settings']) ? $atts['settings'] : array();
    $menu_position = isset($settings['menu_position']) ? $settings['menu_position'] : 'left';

    $icons = isset($atts['icons']) ? $atts['icons'] : '';
    $cube = isset($icons['cube']) ? $icons['cube'] : '';

    ?>
    <p>Custom html</p>
    <?php

}

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Remove default hooked functions

remove_action('product_designer_editor', 'product_designer_editor_notice', 0);
remove_action('product_designer_editor', 'product_designer_editor_panel', 15);
remove_action('product_designer_panel', 'product_designer_panel_main_tabs', 10);
remove_action('product_designer_panel_tab_content_assets', 'product_designer_side_list', 15);
remove_action('product_designer_panel_tab_content_assets', 'product_designer_panel_clipart', 15);
remove_action('product_designer_image_type_content_clipart', 'product_designer_image_type_content_clipart', 15);
remove_action('product_designer_panel_tab_content_assets', 'product_designer_panel_text', 15);
remove_action('product_designer_text_type_content_text', 'product_designer_text_type_content_text', 15);
remove_action('product_designer_panel_tab_content_assets', 'product_designer_panel_shapes', 15);
remove_action('product_designer_panel_tab_content_editor', 'product_designer_panel_tab_content_editor', 20);

remove_action('product_designer_tools', 'product_designer_tools_editor_actions', 20);
remove_action('product_designer_tools', 'product_designer_tools_object_list', 20);
remove_action('product_designer_tools', 'product_designer_tools_edit_text', 20);
remove_action('product_designer_tools', 'product_designer_tools_edit_img', 20);
remove_action('product_designer_tools', 'product_designer_tools_edit_shape', 20);
remove_action('product_designer_tools', 'product_designer_tools_product_info', 20);
remove_action('product_designer_tools', 'product_designer_tools_keyboard', 20);

remove_action('product_designer_editor', 'product_designer_canvas', 25);
remove_action('product_designer_editor', 'product_designer_scripts', 30);
remove_action('product_designer_editor', 'product_designer_loading', 35);
remove_action('product_designer_editor', 'product_designer_welcome_tour', 40);

remove_action('product_designer_welcome_tour_content', 'product_designer_welcome_tour_content', 10);
remove_action('product_designer_editor', 'product_designer_preview', 45);
remove_action('product_designer_panel_tab_content_templates', 'product_designer_pre_templates_promo', 15);
remove_action('product_designer_editor', 'product_designer_toast', 50);
remove_action('product_designer_editor', 'product_designer_editor_style', 90);