Wouldn't this kind of transaction require a software support?
Yup, this is why it would be a hard fork. But it would not need 51% of anything, you would create Bitcoin2.
No. 51% can only make a Denial of Service attack.
It cannot send bitcoins to another wallet. You still need a private key to do that.
Wrong. You can go back in the blockchain and rewrite the block wich created the coins used in that transactions and have them mined by you. Since you mined them, you can send them to whoever you want. That is a 51% attack.
But the OP was not speaking about a 51% attack but about a hard fork, wich would create Bitcoin2, exactly like we have namecoin, litecoin etcetc.