You can overload, as long as there are places available in the subjects you want to do. It depends on the faculty. The Faculty of IT won't let you do more than 4 subjects per semester unless its your final semester, because of limited places in their subjects (mostly electives). The Faculty of Business, however, may allow you to do so, because they have more places in their subjects.
They do warn you, however, that taking more than 24cp of subjects per semester (usually more than 4 subjects) means that you will not get any special consideration in exam situations and maybe even assignments. So if you get sick and miss an exam, or something like that, then they won't do anything about it as far as I know, because you are taking more than the recommended load of subjects.