Yes, you can mix and match the module sizes in just about any Mac, so you could even have 4GB +32GB

My previous reply was based on the thought that the SSD in this laptop was a Samsung SM951. I could have sworn that was in the teardown previously, but maybe it was too early in the morning :)

Since the model installed is the Samsung PM851 - a standard SATA M.2 80mm SSD, then another one like the Transcend mentioned will do just fine, as well as the Crucial M550 or MX200 M.2 when they are available.