There is a duel in Barry Lyndon , where one of the duelists faked his own death by loading the other gun with tow. Did this ever happened during the 18/19th century?

I can't think off-hand of any duels specifically like the one in Barry Lyndon, that is to say where the intent was to trick one duellist into thinking they had killed the other so as for the "survivor" to then flee, but there is a rich tradition of mal-loaded dueling pistols which we can talk about! Generally speaking, such occurrences were done by the collusion of the seconds who, for whatever reason, thought that the duellists ought not to get hurt. Loading too little powder, or no bullet at all, were common ways to do this.

A situation such as this has the infamous distinction of bringing about the only incident of a duelist being executed in the United States. Two men in 1819 had a falling out in Illinois, and a duel was arranged. The seconds agreed to load only powder, but one of the primaries caught wind of the arrangement, and surreptitiously put a bullet down the barrel after being handed the gun, and upon discharge, struck his opponent dead. While generally speaking, a jury was inclined to acquit a duellist, assuming it ever went to trial, such an egregious violation of the code of honor, amounting to the knowing murder of an unarmed man was an exception. He was convicted and hanged for the offense.

Such practices were not super common though, or at least the seconds rarely left records of it. The exception would be France in the 19th century, where pistol duels were generally considered something of a harmless affair, more about posing and posturing than any lethal intent. As such, it was practically expected that the seconds would doctor the guns in some way as extra insurance against the chance of injury - the duellists themselves wouldn't request this done, but it was practically expected, not that the duelists would shoot at each other anyways, as shooting far wide was quite common. Mark Twain, in his travelogue "A Tramp Abroad" had this to say about the duels he saw in France:

Much as the modern French duel is ridiculed by certain smart people, it is in reality one of the most dangerous institutions of our day. Since it is always fought in the open air the combatants are nearly sure to catch cold. M. Paul de Cassagnac, the most inveterate of the French duelists, has suffered so often in this way that he is at last a confirmed invalid; and the best physician in Paris has expressed the opinion that if he goes on dueling for fifteen or twenty years more,—unless he forms the habit of fighting in a comfortable room where damps and draughts cannot intrude,—he will eventually endanger his life. This ought to moderate the talk of those people who are so stubborn in maintaining that the French duel is the most health-giving of recreations because of the open-air exercise it affords. And it ought also to moderate that foolish talk about French duelists and socialist-hated monarchs being the only people who are immortal.

So anyways, that is the sum of it. Yes, some duels were conducted with guns that would not prove to be lethal, although at least in the cases the duellists knew, or at least suspected it.