Jim Lovell's account of Apollo 13, Lost Moon describes reprogramming the computers in-flight...in machine code. And there wasn't even a Workbench interface, just three digit messages for output. The programs were sent instruction by instruction to the crew, who wrote them down and verified each one - all subject to the delay caused by distance.

The book has so much more great stuff for nerding out than the movie, that it's worth a read.