[balinor]

Unfortunately X-Cart didn't bother to assign a class to that piece of text, so it isn't that easy. This is the line that controls the code, it is in skin1/modules/Product_options/customer_options.tpl:

<td valign="middle" height="25">{if $usertype eq "A"}{$v.class}{else}{$v.classtext|default:$v.class }{/if}</td>

You'll need to either add a class to it, or use <span> tags to format it.