I can’t change my emblem on waypoint 
also they don’t have the grunt emblem in halo 5
Hey OP, do you mean your Halo 5 emblem for use in the game, or your avatar for use here on Waypoint? If it’s your in game emblem then yes, it’s not currently possible to change it via Waypoint. You have to do it via Halo 5. The Grunt emblem might still be in the game, haven’t seen it myself that I remember but it’s possible that it’s yet to be revealed or it’s found at a higher level 