Customize the “Available for back order” text for specific variation

I did it.

The “stock.available-on-backorder.step-1” is the css class of the availability text ( Available- made to measure

).

<?php 
add_action( 'woocommerce_before_add_to_cart_quantity', 'made_to_measure' );

function made_to_measure() {

   global $product;

   if ( $product->is_type('variable') ) {

      ?>
      <script>
      jQuery(document).ready(function($) {

         $('input.variation_id').change( function(){
            if( '' != $('input.variation_id').val() ) {

               //var var_id = $('input.variation_id').val();
               var pa_size = jQuery( "#pa_size" ).val();
               if (pa_size=='l' || pa_size=='xl')
               {
                $('.stock.available-on-backorder.step-1').html("Available- made to measure");

               }


            }
         });