Amateur built airplanes are the same way. *You have the plans. *You can
change anything you like.

You paid for your airplane plans (or not) -- change them all you want.

You *might* have paid for your Linux distribution. You can change it
all you want.

You can fly in airplanes running open source software for their
control systems and avionics. And you can change that software too.

I have *nothing* against anyone building any contraption they like to
fly in (as long as it doesn't fall on me or mine).

But I value my skin too much to fly in or build just anything some
random amateur has designed. Software, that's one thing. If your Linux
kernel crashes because you you have a dangling pointer somewhere, so
what? Just reboot. Unless that software is controlling your
elevator ...

And aircraft? Anyone who's spent a little time reading even the basics
of aircraft design should realize it's very tricky biz.

Hat's off to you, though. I'm all for the experimental category.