[tbworld]

I am not sure exactly what you are trying to do, maybe this will help you clarify your question.

A vbulletin style consists of HTML for structure and CSS for visual presentation. You will find them in the ACP (admincp) templates section. Each displayed page on vBulletin might use several templates and several CSS files. The vb style manager allows you to have a different set of HTML templates and CSS files (stored as templates) for each style you create. It uses a hierarchical system so that it knows to use the parent style if you have not altered a particular HTML template or CSS template within your custom style.

That being said, there is no reason you cannot alter areas of your board by overlaying CSS from an external file, this is a common practice. One board that I worked on we replaced all internal CSS (templates) with a single external CSS file, so we could use LESS (a css compiler). It was an interesting project, but the way vbulletin handles their CSS turned out to be a more efficient method.