How much modification can I do in the base theme?

[Audun MB+ 17]

We've used PlatformPro for some websites in my organisation, but for the main site we've used another theme that has been set up by a designer. While the designer was good enough, the theme he used to build our website on is a piece of crap (shitty and buggy code). Still I like the design and some of the functionality of the current theme. So I was thinking that it might be possible to use Platform Pro and build a base theme that incorporates much of the same elements that the current design does. Is that possible? Site: http://www.attac.no

[Kate 3]

If you (or your developer) are comfortable with CSS, PHP, and the framework, you can do most modifications (within reason).