How to filter a wordpress core function?

by

This worked for me:

function uploader_text() {
    ?>
<p class="upload-html-bypass hide-if-no-js">
    <?php _e('mytext here'); ?>
</p>
    <?php
}

remove_action('post-html-upload-ui', 'media_upload_html_bypass');
add_action('post-html-upload-ui', 'uploader_text');

You tried to do “remove_action” after the action already happened. That was the bug.