[robryk]

All of the code was in read-only memory (core rope), so it was impossible to modify it.

There was at least one case when the behaviour of the code was significantly changed in flight to work around a hardware failure (shorted button). This involved changing the writable memory, which kept all the state, to selectively disable some parts of the lunar landing program. For more details see:

http://www.ibiblio.org/apollo/#Final_exam_for_the_advanced_s...