Change slide orientation from landscape to portrait

A single slide? no. The slide dimensions/orientation are set per-document, not per slide, so all slides will be the same.

What is it you're trying to achieve? I'm not sure I can envision a scenario where the slide orientation changes mid-presentation. Knowing what it is you're trying to achieve might surface alternative options.

For example, if it's for visual effect, you might be able to achieve the same result by setting the slide to a square and using letterboxing (black rectangles at the top/bottom or left/right to mask the visual appearance of the slide. If you're looking for handouts/printed media you could rotate the content on the slide, export to PDF and rotate the specific slide/page in a PDF editor...