I guess if you go over the quota for your package, it ups you to a package to match your usage, and uses up any "Rapids" in your account at the rate for the new package. You can, afaik, manually switch down at any time to a lower or even "zero" package if your usage permits it, but I'm guessing they haven't implemented automatic switch-down. Also afaik, there is no automatic rebilling on RS, you always had to manually make any payments up to now, and I doubt they've changed that except maybe as an option for the Business package.
I guess if you go over the quota for your package, it ups you to a package to match your usage, and uses up any "Rapids" in your account at the rate for the new package. You can, afaik, manually switch down at any time to a lower or even "zero" package if your usage permits it, but I'm guessing they haven't implemented automatic switch-down. Also afaik, there is no automatic rebilling on RS, you always had to manually make any payments up to now, and I doubt they've changed that except maybe as an option for the Business package.