First time Swiss Air flyer.

If you buy a full economy fare, do you immediately get the option to upgrade to Business? I wanted to fly Business outbound BOS-ZRH and economy back (mainly to sleep on the overnight outbound) and immediately after purchasing, I noticed option to buy upgrade on return flight for around 50% of what it would cost to buy business outright ($600 economy fare + $900 upgrade vs $3000 business if purchased initially). Thinking I should take advantage of 24 hour cancellation policy and just rebook with full economy fare roundtrip and just pay for the cheaper upgrade...

Seems like a weird loophole unless I'm missing something... Thanks.