¿Cómo reemplazar Let's Encrypt RSA de 4096 bits con ECC de 256 bits?

[mpalmer (Matt Palmer)]

I’m ambivalent on documenting it. The benefits of wholesale replacing an RSA certificate with an ECC one are so niche, and the potential downsides so great, that we’d probably end up with more “I did this thing without considering the consequences AND IT’S ALL YOUR FAULT” topics than “I have a legitimate use case for an ECC cert but can’t figure out how to modify the template to make it happen”.