How can I change my name using command blocks?

Solution 1:

There is no command to change a player's name.

As a workaround, you could fake it by hiding the player's name whilst teleporting a named entity onto them.

To hide a player's name tag, put them on a separate team and change the nametagVisibility option:

/team add HerobrineTeam
/team modify HerobrineTeam nametagVisibility never

Then summon a named entity, such as a marker armorstand:

/summon armor_stand ~ ~ ~ {CustomName:'"Herobrine"',CustomNameVisible:1b,Marker:1b,Invisible:1b}

You can teleport that entity to the player on a clock with something like:

/execute at @p[team=HerobrineTeam] run tp @e[type=armor_stand,name=Herobrine] ~ ~1.7 ~