That Bob Justman memo reminded me how much fun they had making TOS (as well as working long and hard of course). Perhaps my favourite is the memo chain Justman started about Vulcan proper names.
Re fixing mistakes: I guess I don't have a problem with it as long as the mistakes are trivial, are clearly errors, and the original version remains available. What constitutes a "trivial error" of course can be up for debate. Correcting a background audio cue - sure, why not? Changing early TOS references of "Vulcanians" to "Vulcans" - definitely not.