I added your theme to my test site and I did not find a way to do this without disrupting your whole page.
However you can take your tag line and add it to your website name with a hyphen so it separates it and makes it different from your title. You can always add a logo or favicon that has it in it anyway.

I was able to add several lines of text to the site tagline area and you could give it a good description from there if you choose to.

San

Hi Aishii, I would make a backup of everything before you start changing anything. That way you have a copy of all your content, pics etc. Just as a precautionary measure. This will make it easier for you if you have to reintroduce anything. Hope this helps.

If you have a lot of pages, prepare to do a lot of work on reformatting.
Other than that, no biggies.

I've changed themes twice on one of my sites and there were no big problems. Things needed reformatting and pictures moving etc., but no big deal. Glyn

I've changed themes, after previewing them, as suggested, and have never had any issues. Good luck with your new one!

I tried to change themes and didn't realize the new theme was a Child theme. There were problems and it wasn't accepted - thought I'd lost everything for some moments. Took fright and decided to stay as is with this website. I will start another website with a new theme later. However, I do believe most people don't experience problems in this area.

There is a preview option. And you will probably have to install banners again.

Normally it is not causing any problems by just changing the theme.