Friends,
Allow me to speak (and complaint a bit) from experience:
It used to be you could buy 20K/month regardless of your MR balance, and this was something I saw announced 2 years or so ago. I've done it several times. Then I was told very clearly and sternly on Feb 27 that this could be done only when you did not have that balance in account--and they even REVERSED my last month's purchase which I thought was astonishing. As I have separate Personal (Green), Gold, and Plat cards, I simply opened MR account #2 for the Personal card and disassociated it from the Plat.
If the rules have changed again to allow purchase up to 500K per year, that's news to me.