How can I add more text or keywords to a page without affecting the "look" of the page?

The easiest way to insert keywords without affecting the "look" of your site is to use drop downs.

Other places that you can put keywords would be in the description of images and in code that is only visible to search engines. Code that you can use to more accurately describe your page and increase keyword usage would include things such as: schema, open graph, twitter cards, image file names, etc.