I didn't really think about them changing the opening with later releases, but it makes a lot of sense. I was actually wondering why they hadn't just had a different beginning for the first two episodes, and finding out that they did is cool, even if I wish they had put it on the DVD, just to see (even if the cover already spoils it).
B5 did their title sequence in house so they could change them when they wanted such as when a rank changed or of course, when Delenn's change was revealed.
As for the dialog, there's two bits to note. First, and IMO the cause of many instances of dialogue issues was that with only a couple of exceptions, B5 didn't use 'Preveously on Babylon 5 introductions so JMS tried to get what was needed into dialogue. Also, he made the choice to make the style of talk on the show more formal and sometimes it comes over as stiff.
But it's one of the most quotable shows (if not THE most quotable) I've ever watched.