Hevc

No, but it depends upon what you are using for playback? VLC, Kodi, MPC-HC. I use my Sony Television for playback and this seems to work fine.

You can always transcode the HVEC x265 streams with ffmpeg and get back to an x264 file.
 
Any way we can add hevc codec to mag254?

Is it possible to add the vlc, media center classic to mag 254?

Whats the point of downloading x265 only to reencode to watch it on mag, might as well download the mp4 version of the movie.