zlacker

That's incorrect. Allowing internal flashing just requires setting certain parameters in the flash to being read-write, and doesn't require any of the flash modification necessary to disable IME.

Disabling IME can have other impacts, and Purism even has a blog post explaining what the issues were and how they resolved them -- once they figured out what IME modules were needed for their laptop to work properly they could disable IME with a software update.

I don't know if that's how they did it, but you're misunderstanding the difference between disabling IME and enabling internal flashing.