This stuff gets suggested all the time, and I have no idea why people subscribe to this theory.
It's clear that the rules are actual rules, and not some personal bullshit Genie made up.
Genie is pissed at being tricked out of the cave. He's not supposed to hand out free wishes, hence the necessity of making Aladdin "nod" for his second wish.
He has no choice but to serve Jafar when Jafar becomes his master. He *clearly* doesn't want to serve Jafar, but he gives Jafar three wishes that make him very fucking dangerous because he's bound to his duty.
If Genie had the option of murdering Jafar in order to save Agrabah, I'm sure he would have, personal code or not.
Jafar tries to wish for Jasmine to fall in love with him and he can't do it. Not because he refused on moral reasons, but because it was beyond his power to do so.
In the sequal, Jafar tries to immediately leave the vicinity of Abis Mal, but can't because he is bound to serve him. He monkey paws the shit out his first two wishes, but he doesn't outright deny them because he can't.
Jafar also realizes that he CANNOT murder Aladdin. He tries to manipulate shit to get Aladdin executed, but he can't just fry him with an energy bolt himself.
He tries to get Abis Mal to wish him free, because he knows that is the only way he will be free from the rules.
Then in the show, we meet an evil duplicate of Aladdin who has an evil (and retarded) duplicate of the Genie. Evil Genie wrecks Agrabah, but doesn't explicitly kill anyone. Aladdin get ahold of the evil lamp and wishes everything back to normal and the genie has to do so, despite being evil.
Genie's girlfriend Eden re-iterates the no-killing rule when she is introduced. She has no choice but to serve Abis Mal when he gets possession of her bottle, but she still can't kill for him. Nor can she kill him to serve her own interests.
The no-killing rule has shown as an absolute with three, arguably four genies.