Darlene, thanks! Nydia, the profile manager, can work on these after she returns from NGS 2016. In these cases, the Last Name at Birth is correct and just needs the underscores changed to spaces. We could fuss about whether it should be "Ponce de León y Loayza" as on WikiTree, or "Ponce de León y de Loayza" to preserve the "de" from his mother's name or "Ponce de León-de Loayza" as originally entered to comply with a desktop software program that didn't permit spaces, but we haven't come to consensus on a single format for Spanish dual surnames.
It looks like the WikiTree system needs us to change the Last Name at Birth first, as we can't edit the Current Name or any other part of the profile while the Last Name at Birth contains illegal characters.