There is no "standard" way to do this. The common workaround is to have multiple elements - SelectItem
in your case - that are styled differently - and use an expression with the rendered
attribute to determine which ones are visible. This works for any component library, not only primefaces.
EDIT : have tried it right now - looks like I cannot influence the styling of the selectitems at all - at least not declaratively in the page. One could try tweaking the theme or overriding the primefaces selectors with custom styling using !important
rule. But you would still not get distinct styling for the selectitems.
So please excuse my former confidence and regard this answer as a "No, you can't".