Highly Customizable....Means what?

I was checking out your themes. Lots of good ones. In particular, i have a client in the photography industry. I was looking at your PhotoGallery Theme Series, the 5 for 1 combo pack. In the list of features, it lists, highly customizable, stating that you can easily make changes to the general set up. Specifically, i am interested in modifying the header, to contain a more traditional navigation tab at the top. Is this something that is easy to change, grouped in as one of the customizable features, etc? In addition, what other things are highly customizable? I sort of am assuming that you mean there is a feature to make these modifications. I can and have messed with CSS, and a bit of overall theme set up, but im looking to purchase one very close to the end product i am going for, and am wondering if i will be hand coding the changes (highly customizable), or if its built in to the theme. Thanks in advance for your time and help.

Kobra