That shouldn't be a problem. The hopping option is 53.25 per ticket, whether you paid for 5 days or 7 (or 1 or ten). You should be able to upgrade at your resort or at any of the parks.
Typically the advice is to use the ticket at least once prior to upgrading to lock in the discount. I don't know if it would matter since you are adding hopping instead of days, but you could use the ticket the first day then upgrade that day if you hop that day.
The price difference between a 5-day base ticket and a 7-day base ticket is only about 6.50, so I'd upgrade whenever it is convenient for your schedule.