This mod is not known to work with the latest version of Kerbal Space Program. Proceed with caution.
Unzip into your GameData folder, same as any mod.
Just play KSP! The mod is deliberately minimalistic. It adds no UI, it doesn't require any special actions to use. It just silently makes the crew-assignment experience better.
The only thing that affects you at all is: if you go into the "crew" tab of the editor and change crew assignments, then your choices won't be persisted unless you hit the "save" button before launching the ship. That's it, that's all there is to know.
The mod works with two types of assignments: default choices, and player choices.
Default choices are controlled by ModuleManager config in a file that comes with the mod (see "How to customize", below). There are two flavors of default choices, assignments and requirements.
Assignments are default choices for crew slots in specific crewable modules. The default config that comes with the mod assigns scientists to science labs, and all crewmembers to command pods. The default config deliberately leaves passenger cabins empty, though you can tweak this by adding your own config if you like.
Requirements are added to parts that are not themselves crewable, but which need a particular type of kerbal to operate them. If your vessel has any parts that specify requirements, then the mod will try to ensure that at least one of the specified kerbal type is present in the crew. The default config that comes with the mod adds a "scientist" requirement to all non-rerunnable science experiments (Mystery Goo, Science Jr.), and an "engineer" requirement to ISRU units and ore drills.
When you load a new ship, or add a new part, then everything is controlled by the default behavior and assignments will be updated dynamically as you switch stuff around on your ship. It can do this because you haven't observed the assignments and it's therefore free to shuffle assignments around without invalidating any of your choices.
However, the moment you switch to the "crew" tab in the editor and see what the assignments are, it then nails all the assignments in place. (It's a Heisenbergian sort of thing.) Basically, what it's doing is assuming that the moment you see the assignments, they become your conscious choices rather than something the program assigned.
Once you see the assignments (and make any changes of your own), those get persisted to the ship, and will be saved when you hit the "save" button. Such specific choices are assumed to be for a specific kerbal, or for a kerbal of that profession if the kerbal isn't available.
Since all crew assignments/requirements are controlled by ModuleManager config, you can add your own .cfg file to change the behavior to whatever you like.
If you'd like to customize the behavior, the following references may be helpful:
Many thanks to sarbian for a small but vital bit of advice that unblocked the completion of this mod.
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