The end of the last scene of "False Witness" was not scripted, it was a prank played by Geraint Wyn Davies according to Word Of God. The giveaway is that Nick is 'vamped', but does not have golden eyes, as he does every other time his fangs are out.
Season 3 was going to shift attention off Nick's quest for humanity, but Wyn Davies threatened to quit if all the changes were put in place. Natalie was going to be written out as well as Janette, but only Janette was cut. The PTBS felt neither was young and sexy enough*
which just goes to show said PTB must have been *blind*....
for their target demographic. John Kapelos left at that time because he wasn't interested in Schanke becoming a captain-it would have cut his screen time back too much.
Originally, the final episode was going to end with the closing lines of Romeo and Juliet spoken by LaCroix:
A glooming peace this morning brings
The sun, for sorrow, will not show his head.
Go hither, to have more talk of these sad things.
Some shall be pardoned and some punished
For never was there tale of more woe
Than that of Juliet and her Romeo.
This was cut because of fears it would hurt the show's chances in syndication.
The boy in "The Human Factor" was Geraint Wyn Davies' son, Galen.
Almost-relative: The vampire hunter in "Bad Blood" was Catherine Disher's boyfriend at the time. She was actually pregnant with his child during part of season 2, but lost the pregnancy. By the series' end, she was again pregnant, this time with her son.