I Tested the altar of Tast, in Gazluk City. It correctly rejects non-HC players with a message saying you must be in hardcore mode to use the altar. Once HC, I could use it, and it gave me the buffer (Tast's Boon, +5% to Max Health and Max Power). Then I died (in GK, not very smart but I managed to get back to my tomb) and sure enough the buff was gone.

However, if you return as HC to get the buff again, then turn off hardcore mode in Serbule, the buff stays. I'm not sure if intended or not, but worth mentioning. Serbule is just one word of power away...