No one knows. At least, nobody has reported their results if they tried. Technically, and upgrade is really an exchange of one ticket for another. Neither the ticket you'd own nor the ticket you'd want are being sold. So, there's no telling how much value you'd receive for the ticket, or if you could even get the new one.
I was going to try this myself, but we ended up purchasing annual passes. So, I've still got three 10-day w/ water park tickets that I'll want to add hopping to at some point in the future.