I think the real problem is how you have configured your Dreamweaver site. Maybe I'm missing something in your description of the problem?
to be able to modify the contact form solution pack files using any of the extensions used to create it, the contact form solution pack files need to be at the root of the Dreamweaver site.
You do not need to have Universal Email to be modify the form using CSS Form builder, if you are having a different experience, perhaps it would be more helpful to explore that avenue.
Can you send a copy of the contact form that doesn't work after editing it with CSS Form builder, that may help me understand the true nature of what is going wrong.