Yes. In the images table, find the image you want to edit, click the pencil / “Write manual alt text” option, and type your custom alt text. This works whether you’re using AI mode or Template mode.
When you write manual alt text, that image is automatically locked, so it won’t be overwritten if you change your alt text format or re-run optimization.
If you later want the automatic format to apply to a manually edited image again, just unlock it using the lock icon.