Hi there,
If you have saved your project as A.cptx, then at the time of publishing it gives you the title of the publish project as A (by default), you can change the project title from the publishing screen at the time of publish. Then it will give you the output file as that name which you changed.
If you would like to change the project name (appears in the browser tab while playing the published project), that can be changed from edit> preferences > Project > information.
Thanks.