Upgrading from Gold to Platinum For Bonus Points Then Cancelling?

Hi guys

I was looking to upgrade my account from the Gold membership to a Platinum membership as I have a large purchase to make 10k - which would meet the criteria for the upgrade bonus of 75,000 points for spending 10k)

The gold membership is perfect for me as it is but there isn't really a requirement for me to keep the platinum card long term

Would it be possible for me to upgrade my membership from Gold to Platinum, making my £10,000 purchase and then downgrading my account from Platinum back down to Gold? Or would Amex remove my bonus 75,000 points for £10,000 spend if I did this?

I'm seeing conflicting statements on here from people saying they wouldn't remove the points, and then others saying they would.

Anyone got a concrete answer please?

Thanks