Changing pin direction without glitching on LPC800
You're over-analysing this. There are two registers involved in a GPIO pin, the output data register, and the direction register. Both of these are writable at any time (and I agree your Section 7.7.2 quote does not make this super-clear.)

The remark on p68 doesn't care about a transition, it cares about a power-optimised stable end state. Changing the order makes no real difference, but is cleaner as you describe.

There is no changing from 1 to 0 over a sub-microsecond duration. When you enable the output, it takes the driven value in just the same way as if you drive it from 1 to 0 using the data value.

It is only when the reset data value is 0, the tri-state is pulled up, and after enabling the output you write 1 to the data pin that you would see a pulse.

All peripherals are different, but for example


  A read from GPIODATA returns the last bit value written if the
  respective pins are configured as output, or it returns the value on
  the corresponding input GPIN bit when these are configured as inputs.
  All bits are cleared by a reset.


Specifically, the last write and not the last write whilst the pin direction was set as output.