DS9: "Sons of Mogh":
KURN: I have never understood you, Worf. But I do know this. In your own way you are an honourable man. (Kurn passes out.)
WORF: And you will be an honourable man again, but not as my brother.
Above implies that Kurn did not know what was about to happen to him and that this was a unilateral decision by Worf.
WORF: What will he remember?
BASHIR: He'll know he's a Klingon, and how to speak the language, and virtually everything he needs to know in order to survive, except who he is. And that's the first question he'll ask. Who am I? Do you have an answer?
WORF: There is a man named Noggra, a friend of our father's. He will be arriving in a few hours. He has agreed to provide Kurn with a new identity and a new family. He will supply Kurn with all the answers he needs.
BASHIR: Are you absolutely certain about this, Worf? Once I've erase his memory engrams it'll be almost impossible to restore them. He won't remember you or anything about his real life.
WORF: It is the only way. You may begin.
Again by Worf asking Bashir about the procedure while Kurn is on the table unconscious implies that Kurn was not consulted about this procedure beforehand.
Bashir is a Federation doctor that took a hippocratic oath. Part of that oath is to do no harm. Most people wouldn't want their family doing an elective procedure on them without their consent. In fact, most people wouldn't want any procedure done on them without their consent. (especially one to wipe their memory)
Kurn was effectively stipped of his very being, his memories, everything that made him who he was. Bashir even said it, he won't remember anything about his "real life." He became an empty shell, basically how Klingons refer to their dead.
He didn't really get his honor back, his soul and/or lineage did not change. Plastic surgery, some DNA changes, and wiping someone's memory doesn't change their soul. Although this is not my question, it is something to consider.
I can't believe Sisko would allow it to happen on DS9. There has to be some Federation law against something like this. Telepathically reading someone's mind without their consent is illegal in the Federation. Remember in the same episode Sisko reams Worf for trying to kill his brother to regain his honor, which clearly is a Klingon ritual. Bashir had just saved Kurn earlier thereby stopping a Klingon ritual before it ended.
Even the way they did it was sneaky. If they had asked Kurn, there's a good chance he'd say no. There's no honor in living a lie. What a horrible violation it was.
The Federation is supposed to be an enlightened advanced society.
In light his hippocratic oath to do no harm, existing Federation law, and Kurn's civil liberties, how could Bashir possibly perform this operation without Kurn's consent?
STU, EU, and writers notes are welcome. Anyone with knowledge of Hippocratic oaths or Federation law would be helpful as well.