To the op I guess the question is what are you actually trying to get? First I’d say that chances are your flight may well be on time or sufficiently on time for you to make your connection.

if it’s so late that you couldn’t and you are automatically rebooked then I’d argue no airline can force you to take a flight you didn’t book and you’d thus have no issue saying you want to abandon that last leg and get your baggage. If anyone insists you have to fly, imho, you’d be on strong grounds to refuse.

however, when you mention trying to move your lhr-osl to a different date, it’s a very different proposition. For QF/ba’s purposes, you didn’t have trips from sin to lhr and from lhr to osl, you had a trip from sin to osl and asking to treat the lhr-osl as separate is certainly stretching the logic of the ticket. My guess is that if you want to move to a different lhr-osl on the same or next day, they will say yes, if you ask for it to be moved beyond that, you’d be asking for an exception and not something you’re actually entitled to, and agent/supervisor discretion will apply.