To close the loop, and consistent with a previous poster's experience, when I reached out to the hotel with a request to upgrade into the (lower class) Prado instead of the Toscana, I was originally denied (after the agent reportedly "checked with the reservations manager"). After pointing out that such a policy made no sense, the rep asked to call me back after checking further. Later that day I received a call indicating they were "making a one-time exception" and confirmed the Prado for me.

So, ended well, but surprisingly involved. (Nothing, however, compares to the Kea Lani in terms of hoops one needs to jump through to get a suite upgrade confirmed.)