Say you were developing a website, and once you get the first real life visitor, you can't SSH in any more; it's set in stone forever. Would you swap out a JSON parser on your backend just before you ship? They're functionally equivalent, and should be interchangeable, right? Your unit tests say it's fine, so what's the problem?

Any kind of change is adding risk to a project that costs billions of dollars.

The rover a one of a kind project, and any issues are set in stone before any kind of real world testing can be done.

If anything, the team should be praised for being conservative enough that they managed to pull it off with success.

You're right that dropping an extra 20 megapixel camera in there would be less risky than changing the main lens; but it's still an unspecced addition to the plan. I don't blame them for choosing not to.

In the future when launch costs are cheaper, people with a hacker approach are going to make rovers on their own. Lots of experimental designs, safety in numbers, and they'll do amazing things.

But when you've got one shot, your risk profile makes you conservative in the extreme.