anything can be changed depending on your ability - not a facetious comment!.
PS 3 is an out of the box working ecommerce store and as such comes with few if any options to change things.
However if you are happy with CSS you can chgange most of the colours and fonts. Theme it will do it as well.
If you are really happy with html and css you could create a complete site to yoru own design and then copy WA code to yoru own page. Thats a bit if a task and you wouold have to make sure that you named pages all the same etc.
PS3 is template based so your best move is to do the following.
Make sure everything is working out of the boxwith n o changes, emails, paypal etc etc
Then in dreamweaver modify the templates for each page type testing fully at each stage. Take lots of backups ;-)