update 6/24/17 This process also works on the AP.
With the roll out of the new MDE, there has been a lot of questions about how to check for availability in another park without losing current FP selections. From all the discussion, I thought it was not possible without canceling the first set of FPs. However, with some recent trial and error, I discovered it can be done from the browser version of MDE. Sorry I don't know about the APP. Here is a PDF of how I did it. Hope someone finds it helpful.
It was too large to upload so here is a link to my google drive for viewing.