Can I open exact image from Library back into Firefly to change the style?

There are two ways to get back to the Firefly image page with the prompt and styles.  They are both in the upper right corner of the image. Clicking favourite:

will save the image, prompt, and styles in the browser. It is then available from the Favourites link on the Adobe Firefly home page. The disadvantage is favourites are only saved in the browser of the computer you are using. They are not centrally stored. So if you change browsers, clear the broser cache, or use another computer, you will not see what you saved.

The other is to use the Download button:

and then select the Copy link option:

This copies a URL into your clipboard.  You can then paste that URL somewhere to store it (some people use spreadsheets of URLs to track images previously generated).  Going to the URL takes you back to the generation page with the four images, prompts, and styles.

If you have not saved an image using one of these two methods, you cannot return to the page with the image, prompt, and styles.  Meaning, saving the image in your library only saves the image itself—not the prompt and styles.