That’s a really weird error. I’m not quite sure of why you are getting that error to be honest. As @sjr04 said, you can just use the CharacterAdded() event. It’s the simplest way. Just do this:
You don’t need to change anything to not confuse NPC’s, you can use this single line to fix that.
--I'm assuming that you have your variables already done.
if Humanoid and UpperTorso and v ~= script.Parent then --I'm assuming the game is R15
--Continue your code
Also no idea why you want to just change the name.
Maybe you mean the DisplayName?
Changing the name doesn’t change anything, you wanna change the DisplayName.
Alright, there’s a script I have that makes an NPC rotate towards the nearest Humanoid, but then I realized that would include players, so when I tried to change it it wouldn’t work.
--I'm just adding some code that might not work, but it also sorta makes sense.
if Humanoid and UpperTorso and v ~= script.Parent and ~= Player then --I'm assuming the game is R15
Edit: Do players in your game have a specific tool that no NPC has?
It’s an old post to be replying to, and why? When you morph that only changes the character appearance, like body type, accessories and clothing etc. The humanoid isn’t and shouldn’t be changed at all. Why would you want to make the player renamed to “Humanoid”?