Can I embed a CSS class in another?

Hi
We are trying to roll out a new font across a website. It's been built whereby a class like .title-big has the font-family name assigned to it.

Therefore we have a lot of these hardcoded font families within the style sheet. Ideally we'd like ALL the font families to be at the top, so there are less to edit once we go live with the font.

At the top we have new classes like: book, thin, medium, strong, bold.
So where html is like this:
<h3 class="title-big blue">Hello there</h3>

We are changing it to this:
<h3 class="title-big blue book">Hello there</h3>

So the Font Family is removed from .title-big, and takes on the class of "book" which is at the top of the CSS file, with the font family.

It would be rather useful if we could find these classes and add "book" to that class in the CSS file, which would mean we don't have to update ALL the pages that use that title-big class.

Any ideas?
ps. this is in WordPress.