Please answer - PINs after New Year? :(

As you all know, RWT is basically impossible to do safely after January the 1st 2008, due to the introduction of unbalanced trades. The only thing I use the Runescape Black Market for is to buy PINs for my main's membership. So I guess I'll buy a lot of PINs for membership before the New Year comes. I have a question regarding this though:

Is it possible for me to buy like 2589275829 valid PINs (any PBP or SMS) and use it each month on ONE character (I'm only using membership for 1 account). In other words, is there a limit to how much PINs one can buy and use on one account each month - in essence, do PINs have expiry dates for each account?

Example: I buy 12 PINs to use on Zezima (not my account, jsut an example). After one month I've used up 1 PIN and so I use one of the others that I bought earlier. Now I have 11 PINs, and when I run out of that month of membership, I'll use another PIN for membership, and so on, repeat repeat repeat.

Thanks (If you answer)!

P.S.

To counter both of these issues, is it possible to just apply all the PINs you have bought on one account at the same time. Example: You buy 5 PINs and apply them all to an account so that your account will stay a member for 5 months, instantly renewing membership immediately after one month expires, like how it does for credit cards

 

There like is no good way to buy pins after like impossible.