Using CSS Sculptor you can customize the SiteAssist Pro layouts with the presets. There is a How To on using CSS Sculptor and Menu Writer together to create custom layouts for SiteAssist Pro, here is a link to it:
It can be found on the SiteAssist support page in the How To area, here is a link to the support page:
The reason that we make these presets available is because of the many requests we have had for them in the past. You can use them in conjunction with the tools to customize the SiteAssist Pro layouts or you can use the source and completely customize then to fit your own needs. The files are meant to be loaded into the preset manager for CSS Sculptor.