Unless you cannot use a reseller, like
Undercovertourist, or even just on Universal's web site, buy the ticket you want, and just book the room. separately. Any package of tickets and room, has a change free, and cancellation fee that has a longer than 5 day before arriving day, get your money back. A room only, loose the night's deposit, if not cancelled before 5 days of arrival day.
Is there a discount, like Mac says, for booking the package of tickets and room? I'd price buying them separately, to compare.
Your room key is your express pass, and the hotel does not care, nor does Universal, where you buy your park tickets for.
And, if you want to visit both Islands and the Studios on the same day, you need a park to park ticket. A 2 day park ticket would most likely be one park a day, and no hopping or riding on the Potter train.
If you are hitting the parks for only one day, I'd make sure it's a one day, park to park ticket. And make sure you can use it that time of year, as now Universal dos change ticket prices depending on when you are using them.
Enjoy the HR, it is nice hotel, and a short walk or boat ride to the parks, walking path is nearest the Studios.