If Hard Fork really happen, and if one wants to take advantage of selling one of these (BTU or BTC) and focus on the other, how can that be done? Can this be done by bitcoin-qt and bitcoin-unlimited-qt for each "coin"?
BTU has its own client, so what you have to do is having all of your coins in bitcoin core or any private keys you control.
As the hard fork happens, you will have the same amount of BTU you have of BTC.
Then what you do next is dump BTU on an exchange, wait for the storm and celebrate the free BTC as BTU collapses by its own weight.