If I run the following PHP code on node-product.tpl.php:
str_replace('Quantity','Quantity <a id="increase_val">+</a>/<a id="decrease_val">-</a>',$content);

When the page loads, if you look at the raw HTML, it has updated, however on the page it has not, as inside uc_aac it deletes the form and recreates it:
uc_aac.js line 19-26 (I think)

if (data.form) {
        var action = form.attr('action');
        $(form).after(data.form).next().attr('action', action);
        console.log(data.form);
        form.remove();
        Drupal.attachBehaviors();
      }

I am not sure what this is for, but once I comment it out, the overrides or any changes I have made to $content, stay there.

Not an issue as such, but a fix if anyone else ends up here.