Can you upgrade Disneyland tickets more than once?

The current 3 day-1 Park per Day tickets only let us go to one park each day but we would like to upgrade them to park hoppers. Can we do this and THEN upgrade them again on the third day or is there a ONE time upgrade rule?? I ask this because we already used ONE day up at Disneyland and would like to upgrade to hoppers on our SECOND visit but we are still undecided if we want to go all the way and upgrade to Annual Passes on our THIRD and final visit. Has anyone tried upgrading Disneyland tickets more than once? If so, where do you go to do the upgrading? Thank you!