You would have to modify the theme files by switching to a child theme. I would not recommend adding too much there. Seasonal Pro does not have a sidebar in the side column area due to lack of space, and also the overall design concept of this area because some people may have smaller screens.
That’s great, thanks. Using the child theme not an issue.
Related question. Is it possible at all to use html behind the tag. Using the tagline to show the telephone number and having it as a clickable link under the menu would perfect. With so much use of mobiles these days then the ability to click a phone number and have it ring is the only thing missing here.