I managed to beat blood Undefendable without killing any New Jericho Units and was a bit bummed out to discover that doing a bloodless (I did shoot a fews arms) end to the mission doesn’t change the -10 New Jericho standing. I’m a bit mifffed as it took me almost an hour to get it just right.
The -10 New Jericho Standing is one reason I skip that mission. I also believe that it is a steal research mission with infinite reinforcements arriving on the map every turn, and I tend to avoid as many missions with infinite reinforcements as possible. I really hate the infinite reinforcement mechanic because it tends to make every mission drag on and become super tedious and boring.
I’d also recommend to skip the mission considering you get the tech anyways from having good relations with NJ.