No extra armour was ever added to the Tiger II.
At 68 tons it was heavy and the armour at that time was good enough to beat most (but not all) tank mounted weapons.
There were plans to upgrade the Tiger II with a 105mm main gun, more powerful engine (it was underpowered) and other upgrades such as air con for the crew ets, but this never happened as factories were captured and the war ended before the upgrade would have started.
At this time, the Germans were beginning to consolidate the panzer production process and produce less types and concentrate more on the Panther, Panzer IV and Tiger II. The Tiger I went out of production to facilitate more Tiger II production, altough the Tiger I remained in action right to the last day of the war.
If the Tiger II and the war had gone on and the proposed upgrade had happened then with a better engine and a 105mm main gun and other upgrades the tiger II could have been a very potent weapon on the battlefield especially as they were all crewed by highly experienced and trained combat veterans.
The Tiger II chassis, with some mods was the proposed chassis for the E-series of tanks which would have replaced the Panzer IV. Panther and Tiger II and would have been moch quicker and easier to produce as the majority of parts were the same and as such, interchangeable.