We would like one of the subscriptions with the period 1 year, based on the service plan with option "Charge for Subscription" set to "Before Subscription Period", be billed monthly instead of billing once, on subscription purchase. Is it possible?
No, the option "Charge for Subscription" is a service plan option, it is the same for all the subscriptions based on the plan. The feature request with id #PBA-57732 exists to implement the described behavior.
It is possible to clone the plan, change an option "Charge for Subscription" to "Before billing period" and place an order on this newly created plan.