Yes you can upgrade park hopper to an AP. There are a couple of things to think about first.
AP Prices
PAP~~no black out days, includes parking fee's 219.00
DAP~~Black out days are Saturdays March - August, Christmas week, various holidays. $159.00
SoCal~~Black out most of the summer, Every Saturday, Major school vacations, Major Holidays. $99.00 (do not have to live in SoCal to get this AP)
Check the
Disneyland web site and see which days are blacked out to see which AP works for you. If there is a back out day during your vacation. Upgrade your hopper on the LAST black out day of your vacation. If you get an AP on a black out day, you can use it that day. (If you want the SoCal ap and you are there Thurs-Monday, saturday is blacked out, upgrade on Saturday and you will still get park admitince on Saturday)
You can only upgrade your ap. If you have the 114.00 hopper, you can not get the SoCal ap.
If you will be driving and paying for parking, you only have to upgrade one AP to have parking, PAP or pay 40.00 for parking to be added.
PAP has the most dining discounts. Depending on where you are eating at, you may be able to get the extra cost of the PAP back on dining discounts. Again, only one person needs the PAP to get the dining discounts.
Black out tickets are 25.00. So if a day is blacked and you want to go to the park, you can pay 25.00 to get in.
Hope that helps.