Change the format string to display the entry in a custom format.

add_filter( 'frm_entries_show_args', 'change_entries_show_args', 10, 2);
function change_entries_show_args( $show_args, $args ) {
	if ( 10 == $args['form']->id ) {
		$show_args['format'] = 'new_format';
	}
	return $show_args;
}

Use this example to change the table style from Zebra Stripes to Grid when viewing an entry on the Entries page.

add_filter( 'frm_entries_show_args', 'change_entries_table_style', 10, 2);
function change_entries_table_style( $args ) {
	$args['class'] = 'frm-grid';
	return $args;
}