Some banks allow this, some do not. When allowed, it will not increase your actual limit, but it will effectively have the same impact, as you will have more "room to spend" before triggering a cut-off. Prepayment doesn't alter the awards earned - the type of purchase/charge determines this. Keep in mind that prepaid or not, very large charges often require preauthorization. I spend millions on credit cards through my business each year, but even we run into preauthorization issues at times.