Can i reset emblems on hero currently in raid tourney defense
Yes. You can add and remove emblems during tournaments. It will affect the current hero in your tournament defense in real time.
As @NotoriousDAD said.
Tournament Defence is NOT locked in terms of Emblems. Any change you make during a tournament WILL affect your Tournament Defence Team
Counter to this, your War Defence IS locked in terms of Emblems. Any change you make during a War (after battle phase starts) WILL NOT affect your War Defence Team.