Okay here goes. FCE will not allow (and are very strict) students to overload. Exceptions are made for students in their final year who will need to overload to 'catch up'.
Seraphim: technically, no if the combined degree is administered by the Commerce faculty eg. BCom/BSci. I know with the school of mathematics, they flaunt and bend the rules, and thats fine. I'm not sure about engineering and CSE, but you'll be assured that no life sciences school will overload you - they will all send you to commerce for the official 'no-you-cannot' line.
But yes, you can get around this. As for myself, I have been officially denied overload by both my science and commerce faculties. Thats when a little ingenious becomes quite useful.
So no you cannot overload, if you really want to, yes you can, although now I wish I didn't. I am happy with the fact that I got around the system, theres a sense of satisfaction there, but my marks weren't as good as a result of the extra workload.