Harry like Merlin was later entrusted with the Swords. He must have been considered worthy to be so. Unless the rule is any mortal who comes in contact with a Sword can unmake it regardless if they are a Knight or not.
In this instance Harry was entrusted with the Sword, and like Murphy he failed.
Harry is considered worth to be custodian of the Swords, but that in no way makes him a Knight. Murphy was considered to be worthy of being a Knight for one night, refused any offer to be one full time... However that doesn't make her a custodian, as stated by Uriel and Michael, that she took upon herself.
Harry telling himself he is no knight means nothing. It is all about human free willed choice and the sword can give you the opportunity to choose. And with choices actions have more meaning than wo
You are not taking into account the reaction of the Swords to the person who touches them.. In Harry's case, though he has handled two of the three Swords, they have never lighted up to his touch. The Sword of Faith did light up in it's sheath in the presence of the enemy while on his back, but that wasn't a job offer, and Harry didn't take it as such.. It did light up a little while later when Murphy touched it, Harry immediately took that as a job offer..
Knighthood is not something bestowed upon you, it is a choice you make. And that is the only rule.
No, you've got that a little backwards, the Almighty or one of his Agents have to bestow the Knighthood first... Only then can the potential Knight chose to accept or not accept the job offer for however long... Like Susan, when she touched the Sword of Faith before it totally rejected her, only later in Changes when though Harry she was chosen to a Knight for a night to go and save her daughter did the Sword allow her to make the choice...
And it is not about the final act, the killing of an innocent. Every monster can do that if it is made vulnerable. It is about the first act, making it vulnerable in the first place. No monster can do so.
I believe that is what I said, Harry misusing it made it vulnerable, then Bianca and company could proceed to use it in a sacrifice and unmake it. If it had been stolen from Michael and taken to the party, I doubt that they would have been able to even begin to use it in such a way.
At the moment you pick up the sword, the sword accepts you and you decide to do something with it you are the knight. Even if only for a few minutes. Even if you are not a perfect knight. Even if you tell yourself you are not.
No, Harry kept it on his back on the island even with the idea of trading it for Ivy, but that did not make him a Knight.