Changes Sell Media's terms of service label on Checkout page.

sell-media-custom-text-filters.php

<?php

/**
 * Add the following function to your own functionality plugin
 * or add it to your theme's functions.php file.
 * Change any of the text inside the return value.
 */
function my_sell_media_tos_label() {
    return 'Hey this is my custom text. Please agree to our <a href="javascript:void(0);" class="sell-media-empty-dialog-trigger">terms of service</a>.';
}
add_filter( 'sell_media_tos_label', 'my_sell_media_tos_label' )