I've been wondering if there's a way to, instead of defining the subscription period for each subscription when it is created in the administration section, allow the user to define the subscription period (from a drop-down or something like that) when they choose a subscription. The same would be for quantity, and the price registered at PayPal would change accordingly.

I just wanted to ask if something like this was possible, and if so, where would I begin with altering the module to make it happen.

Thanks in advance.