Two Dogs is also immortal during the payroll ship boarding, the reason being that he is still needed for his own quest. (But his quest is not essential to the story, so he is not immortal at other times. If you get him killed doing non-story things, you miss out on his quest and the Mayan temple quest.)
Likewise, Edmundo is indeed immortal during the convoy boarding. He insists on being there and there can be serious consequences if you get him killed. I thought it unfair to force you to put him in danger and then punish you if he dies. Again, though, he is not protected at any other time, so be careful with him!
You might get away with just copying "PROGRAM\Storyline\Ardent" and "RESOURCE\INI\ TEXTS\ENGLISH\Storyline\Ardent" from the updates to your outdated install, but I make no guarantees. Certainly there is little point in replaying the whole story just to see the museum; the reason for updating and then replaying is to see what happens if you do things differently, e.g. play as Charles, or go through with the kidnap and get the ransom for Edmundo. The other reason for updating the game fully is that "Ardent" is not the only storyline which had had bugs fixed since 2018. You really want to be up to date before you start your next game!
Likewise, Edmundo is indeed immortal during the convoy boarding. He insists on being there and there can be serious consequences if you get him killed. I thought it unfair to force you to put him in danger and then punish you if he dies. Again, though, he is not protected at any other time, so be careful with him!
You might get away with just copying "PROGRAM\Storyline\Ardent" and "RESOURCE\INI\ TEXTS\ENGLISH\Storyline\Ardent" from the updates to your outdated install, but I make no guarantees. Certainly there is little point in replaying the whole story just to see the museum; the reason for updating and then replaying is to see what happens if you do things differently, e.g. play as Charles, or go through with the kidnap and get the ransom for Edmundo. The other reason for updating the game fully is that "Ardent" is not the only storyline which had had bugs fixed since 2018. You really want to be up to date before you start your next game!