Hello,
We haven't added any VCS that reference GEOID12A yet. Vertical transformations aren't supported yet, but you can define the VCS on your data. It's a bit odd on how we have set up the VCS definitions because we use a late-binding method for our transformations. There's a WGS 1984 geoid VCS that isn't connected directly to a particular geoid model like EGM96 or EGM2008.
Melita