While ICH can always turn your application down, as long as there is no defined end date on the certificate, they cannot argue it is no longer valid. And as long as you use it while an Ambassador -- even if it's during the period of membership you received free when you were downgraded from RA -- you don't have to pay the $150 fee. However, if you use it at the end of your current membership period this year, or at the end of your free renewed period next year, you'll only have to pay the regular $100 renewal fee...unless that goes up in price by that time.