I wish I could work out why I can't get multi-quote to work, but as I can't... I just hope you'll all work out which comments I'm following up!
Dayna's tutor/boyfriend in Animals: in the original script, he was Cally's crush, and she was going to stay with him to write Jan Chappell out after the half season she'd agreed to do for season four. When she changed her mind and didn't come back at all, the script got rewritten to give her role to Dayna.
Gan's Limiter: That's an interesting one... the only first season episodes where it really gets a role are eps 4: Time Squad, and 10: Breakdown (there's a small mention in Duel as well, but it's passing). And guess what? Time Squad was a replacement for the original episode four, written alongside episode 10. As can be spotted from the way Gan doesn't have limiter problems when he should do in some of the earlier episodes (most notably, eps 2&3).
And Blake's background: he was an engineer. But I think that's only mentioned in Cygnus Alpha, when he and Avon both spot that what Liberator's teleport system is, because they both worked on Project Aquator, the Federation's failed (but obviously not entirely wrong-headed) attempt to build a teleport ("Small world..." "No, big project").