Hi, Im not quite sure I uderstand the question but...
To override stylesheets I think you just put them in the design/your_site/stylesheet directory.
If you are wanting to change the style based on which node etc you might be in as per the template overrides, cant you just put logic in the template to display different div tags which will reference the different styles you want?
remember to put a reference to any stylesheet you use in the pagelayout.tpl eg:
