if your on the
disney dining plan can you change one day to the deluxe or platinum and then chage back to the regular plan ?
The simple answer is NO, you cannot since you are talking about 2 seperate plans - Disney Dining Plan and Premium or Platinum plans, Each requires its own booking and each has different rules and requirements.
DDP requires at least a 2-day Park Pass purchase. Premium/Platinum require at least a 1-day Park Pass purchase. NONE of the plans allow discounted room rates - all must be RACK RATE.
DDP can be purchased at any resort including DVC; Premium can be purchased at any resort (even Values) but not added to DVC bookings; Platinum can only be purchased for stays at DELUXE resorts.
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Here are some ways you could you add a Premuim plan to your current DDP ressie.
Example: You booked a 7-day stay at POP with DDP and want to make one of those days a Premium Plan. You have 2-3 options:
1-Leave 7-day DDP as is; ADD Premium Plan for 1-nite during that 7 day stay (yes, this gives you 2 rooms on the same night) - Total 7-day stay with 2-day PP and 1-day PP purchase required;
2-Break 7 day booking into 2 seperate ressies (1 & 5, 2 & 4, 3 & 3, etc.); ADD a Premium Plan in place of one night - Total 7 day stay with 2 purchases of a 2-day PP and a 1-day PP purchase (not a good use of Park Pass purchasing!);
3-Leave your 7 day DDP as is ADD the Premium to the first or last part of your stay and not dividing your DDP stay days - Total 8 to 9 day stay with 2-day PP and 1-day PP purchase required;
In any case, you will have to buy those minimu Park Passes for each package AND check-out/check-in when you go from one package to the other. Resorts can generally reference the bookings to each other - on your request at time of ressie AND confirm at time of original check-in - so you do not have to actually change rooms. Only if you do a Platinum while staying at anything other than a deluxe resort would a move be required.
However, you could stay the whole time where you are currently booked on DDP (all 7 days per the example above) and make a completely seperate 1-night Platinum Deluxe resort booking at REGULAR rates. You don't have to relocate and can leave you luggage at current resort, just 'check-in' at the Deluxe resort on the day of your package to get your KTTK for use through the following day until midnight.
Example: package begins on Thursday early morning and is usable through midnight Friday, allows 2 nights of activities, two days worth of tours and 3 meals (appitizer/entree/dessert/beverage even if all are at SIGNATURE dining locations) and 2 snacks per person stretched out over those 2 days, which is very easy to do.
For the package night, take a change of clothes and an overnight bag and spend that night in the Deluxe room, which is especially convenient if it at Poly, GF or Contemporary, with Wilderness Lodge being a decent location as well.
Just booked out Anniversary trip for next year over Columbus Day weekend. So excited! POFQ w/ premium plan. Hoping to eat at the Flying Fish, California Grill, and then an Epcot lunch...maybe Le Cellier! I'm way too far out to book but that's what I'm thinking for now. Looking to do KTTK tour, and the Segway around the World Showcase, as well as Behind the Seeds, Parasailing and some crack-of-dawn golf lessons for DH.
WOW!!! You are my DIS HERO!! This trip is to celebrate my Mama's Birthday and it will be my "WELCOME BACK to WDW, ITS BEEN WAY TOO LONG" trip. 
We will use our 1 day ticket to upgrade for next years passes. We did choose to stay at GF and pay rack rate for convenience and we have never stayed there, so that was an extra cost that we could have avoided by staying in one of the cheaper deluxes. This trip is a once in a lifetime trip for us, so we are doing exactly what we want to do instead of trying to scrimp and save every step of the way like we normally do!
