Hi there,
Thanks for writing in! Usually you need to override the woocommerce template. But here goes a easy solution for you.
You can add this under Custom > JavaScrip in the Customizer.
jQuery ( function( $ ) {
$('.onsale').text("Pre-Order!");
} );
You might need to decrease the font-size since the text is a bit long. Let’s add this under Custom > CSS in the Customizer.
.woocommerce li.product .onsale {
font-size: 10px;
}
Let’s adjust the font-size according to your site design.
Cheers!