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.
From memory Jan was first offered five episodes (leaves with Justin in Animals), then three (killed by Servalan in Traitor) then one (killed by Dorian in Rescue). In the end we got a couple of words.
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).
Providing Gan 'told himself' he wouldn't kill them he was ok. He was able to strong arm the monks in Cygnus Alpha but when it came to the cryo psychos he knew he had to kill them to protect Jenna, hence the pain.