Most automatic transmission cars come with a manual mode these days. Would more wear take place if a driver were to change gears manually regularly?
The simple answer is no.
Modern automatic transmissions which allow manual gear selection have sophisticated controls to maintain efficiency and reliability of both engine and transmission.
You cannot, for instance, select sixth gear when you start from rest nor can you select reverse when travelling at 100kmh.
In fact, the control system basically takes charge in the event of any transmission abuse.
Using the manual mode gives the driver a limited but useful level of control in various circumstances.
A good example is when driving down a spiralling multi-storey carpark - the manual mode can maintain the gear in first to provide maximum engine braking and hence a constant slow speed.