yes.
payment methods can be changed as much as you want, as long as it's before the financial census date.
classes can be rearranged/enrolled as much as you want, as long as it's before the academic census date.
also know that the academic census date is the deadline for dropping a course without having to pay for it, whereas the financial census date means you can drop the course, but you still have to pay for it (if you're going bad and you think you'll fail, you wont get a fail on your transcript if you drop it before the financial census date, BUT you'll still have to pay for it).