Here is the Wordpress Hook Change the add to cart text on product archives
add_filter( 'add_to_cart_text', 'woo_archive_custom_cart_button_text' );function woo_archive_custom_cart_button_text() {global $woocommerce;foreach($woocommerce->cart->get_cart() as $cart_item_key => $values ) {$_product = $values['data'];if( get_the_ID() == $_product->id ) {return __('Already in cart', 'woocommerce');}}return __('Add to cart', 'woocommerce');}