I decided to do a full playthrough once on version 1 before doing any more playing around. That got me 9/23 of the replay scenes and 39% of the CG gallery. I've already looked at the persistent store setup for cg images, and it turns out that the replay coding is even easier. A grep through the code for replay shows a utility routine unlock_replay.
Code:
XChangeRenewal-1.0.1-market/game $ find . -name "*.rpy" -exec grep -iH "unlock_replay" {} \;
./game_original_day1.rpy: $ unlock_replay (1)
./game_original_day1.rpy: $ unlock_replay (2)
./game_original_day4.rpy: $ unlock_replay (16)
./game_original_day4.rpy: $ unlock_replay (21)
./game_original_day4.rpy: $ unlock_replay (22)
./game_original_day4.rpy: $ unlock_replay (23)
./game_renewal_day3.rpy: $ unlock_replay (9)
./game_renewal_day3.rpy: $ unlock_replay (10)
./game_renewal_day3.rpy: $ unlock_replay (11)
./game_renewal_day3.rpy: $ unlock_replay (12)
./game_renewal_day3.rpy: $ unlock_replay (13)
./game_renewal_day3.rpy: $ unlock_replay (14)
./game_renewal_day3.rpy: $ unlock_replay (15)
./game_renewal_day2.rpy: $ unlock_replay (3)
./game_renewal_day2.rpy: $ unlock_replay (4)
./game_renewal_day2.rpy: $ unlock_replay (5)
./game_renewal_day2.rpy: $ unlock_replay (6)
./game_renewal_day2.rpy: $ unlock_replay (7)
./game_renewal_day2.rpy: $ unlock_replay (8)
./game_original_day2.rpy: $ unlock_replay (3)
./game_original_day2.rpy: $ unlock_replay (4)
./game_original_day2.rpy: $ unlock_replay (7)
./game_original_day2.rpy: $ unlock_replay (8)
./game_renewal_day1.rpy: $ unlock_replay (1)
./game_renewal_day1.rpy: $ unlock_replay (2)
./util_functions.rpy: def unlock_replay (a):
./game_renewal_day4.rpy: $ unlock_replay (16)
./game_renewal_day4.rpy: $ unlock_replay (17)
./game_renewal_day4.rpy: $ unlock_replay (18)
./game_renewal_day4.rpy: $ unlock_replay (19)
./game_renewal_day4.rpy: $ unlock_replay (20)
./game_renewal_day4.rpy: $ unlock_replay (21)
./game_renewal_day4.rpy: $ unlock_replay (22)
./game_renewal_day4.rpy: $ unlock_replay (23)
./game_original_day3.rpy: $ unlock_replay (9)
./game_original_day3.rpy: $ unlock_replay (10)
./game_original_day3.rpy: $ unlock_replay (12)
./game_original_day3.rpy: $ unlock_replay (13)
./game_original_day3.rpy: $ unlock_replay (14)
./game_original_day3.rpy: $ unlock_replay (15)
Once again, the replay setup is used by both the original game and the renewal. So it's just a matter of jumping into the console and doing an unlock_replay(num) where num is whatever scene you haven't unlocked yet. This sure beats having to repeatedly play through the game while standing on the ctrl key in order to choose every possible path from the pathing tree.
So I just started a new game of the renewal version (more scenes), jumped into the console and did an unlock_replay(1) up to unlock_replay(23). Exiting back to the title and entering replay scenes showed that everything was there. Then I just entered each replay and hit ctrl to skip through the scene to enable the corresponding cg's. That got the CG coverage up to 85%.
That doesn't cover where this image comes up (so to speak) in the two games. Wondering if they wimped out and left the tgirl stuff out of the replay or whether it was a gag (sic) shot buried somewhere in the story. I don't remember this from the original game, but a code grep showed it gets used somewhere in the day 4 script.
Looking some more, there's a futa ending that appears to be triggered by drinking the green antidote instead of the red one.