Jesin A on "[Plugin: W3 Total Cache] Can i use W3 Total cache plugin with a child theme"

But i can't as i have to modify the header of my theme which shouldn't be done in parent theme.

Why not modify this on the child theme?

Create the following file

wp-content/themes/tempera-child/functions.php

and place the following code

<?php
add_action( 'wp_enqueue_scripts', 'tempera_parent_style' );

function tempera_parent_style() {
wp_enqueue_style( 'tempera-style', get_template_directory_uri() . '/style.css' );
}

Now edit the child theme's style.css and remove @import.