Highly flexible systems aren't mechanistic
But a machine that generates new programs, treats its machine table is a changing object, and shifts between programs would involve auxiliary devices that can't be modelled on the Turing machine (as Dennett presupposes).
Dennett presupposes that a machine that can take the guise of multiple formal systems is a Turing machine.
The need for auxiliary devices that can't be modelled on a Turing machine means that the machine Dennett describes is not a mechanistic model of the mind.
Thomas Tymoczko (1990).