Well, first off, there are no terminator genes in use. Second, any licensing agreement would naturally prohibit any effort to modify it to remove them. There's no getting around the fact that you'd be willfully violating your agreement by starting from the licensed seeds. And even if you could manage it somehow (which you can't), you'd run right into the same regulatory process that Monsanto has already gone through. It'd be much more than $484k for that process alone, to say nothing of development costs.

Small farmers could never fund that sort of effort, and large industrialized farms would be sophisticated enough and have access to legal counsel to know better.

If you modify Windows, it's still Windows.

I never thought the ship of Theseus discussion would come up in the context of licensing.. Yet here we are!

Good luck sequencing plants from visual inspection.

I don't think that's the issue, here