Generally speaking, it is not possible to apply directly for a residence permit or long-stay visa within Belgium if you entered Belgium on a short-stay visa (i.e. a Schengen type C visa). Instead, you must do that from your current place of residence. There are a few exceptions but they do not apply to your current situation.
Furthermore, you current visa almost certainly does not allow you to work from Belgium, even for a foreign employer. In the Schengen area, there is no such thing as a “business visa”, only generic short-stay visas and, while they do cover business visits, they do not allow work without an additional prior authorization.
Furthermore, a type C visa is only for short visits up to 90 days so it's difficult to see how it could be relevant to the rules that apply during your one-year stay one way or the other (that's the reason why you need another visa in the first place!).
Also note that the whole plan might sound sketchy to a consulate: If you intend to do more than incidental work during the holidays and you apply for a work permit, it looks as if you won't really have time to study and therefore do not have a valid reason to apply for a student visa.
