一年一张绝对没影响。insurance will cover the cancel fee up to the full value of the trip if you can provide valid reason that you can not go, such as family mumber's illness or cannot connect to flight because of the weather, etc. You can not say that you just do not want to go.
You need to cancel it first and wait for about 2 months, then apply again. You will get bonus points each time that way. You will not get bonus points if you apply for a new one before you cancel the old one.