Hello,
What version of phpdocx are you using? Your username doesn't have any license tied, please send to contact[at]phpdocx.com the username or email of the user that purchased the license you are using.
Custom paragraph styles can be applied to paragraph contents, not to span contents. In the case of replacements, custom paragraph styles are block contents, so inline replacements can't be done to apply them. Please check the following sample included in the package: embedHTML/sample_4.php that illustrates how to use custom styles applied to HTML contents.
To add tabs when transforming HTML, a Premium license with HTML Extended is recommended:
$html = '<span>My text content&#9;with a tab.</span>';
$docx->embedHTML($html, array('useHTMLExtended' => true));
$html = '<span>My text content&#9;with a tab.</span>';
$docx->replaceVariableByHTML('TABS', 'inline', $html, array('useHTMLExtended' => true));
Regards.