I've been doing this a lot... refilling a pre-filled with another flavor, without rinsing the carto beforehand. Try to refill with a complementary flavor though, or you may end up with something horrid. I'm refilling menthol, Kant, coffee, chocolate, cinammon bun with 555 which seems to make the flavor mellower. I've also tried refilling menthol with French Pipe and, there is possibly nothing this fp will mix with (it's not to my liking, anyway). I think 555 or most any of the tobacco flavors will mix well with just about everything.