A trade mark class groups products and services that are similar or are in shared areas of trade. So class 43 covers all types of food service from takeaways to top restaurants and hotels. And class 25 covers clothing from high street ready to wear through to haute couture. As the classes system was devised when much of the economy was manufacturing rather than services, and before electronics and computing the class system is lopsided towards Goods with 34 classes, and the remaining 11 cover cover all services. Class 9 is a massive catchall class for technological products, from computer hardware to contact lenses.
No, you cannot add classes to classes to a trademark filing or registration. To have rights for otehr Goods and Services requires a new separate application.