Elon always sends emails out to everyone in the company...These get leaked all the time.
All it would take is a single email:
"There is absolutely no way to retroactively add a referral code to orders. Please stop telling people that it can be done, and that you will take care of it. Instead, suggest that you can cancel the order, and place it again using the referral code."
I'm fine with the policy as is...it's the misinformation, and broken promises that ruin the experience. In my case, it was the Tesla employee's mistake, not mine. He was told to place an order on my behalf, and given the referral code that I asked him to use. He didn't. He was told/reminded of this immediately, and instead of canceling and re-entering, he told me he could just fix it. You can guess how that turned out.