Add validity for "next year"

I saw in the older forums that you can modify the subscriptions plugin to add a "4 year" validity range by editing an xml file:
See old forum post

I would like to add a validity for next year only.
So basically any new or renewing user would pay the "first period" fee, and then next year, the "regular price" would be a higher amount.

How would I add this functionality?

CBSubs supports an initial price and duration separate from regular price and duration. Under the Pricing tab set "Is the first amount and period different" to "Different first period and price for Registration and Upgrade". You can now configure an initial price and duration (e.g. $25 for 1 year) then for regular price adjust it as needed (e.g. $50 for 1 year).

Does this also apply to renewals?

If someone renews this year, I'd like them to get the "current year price." So if they renew in January, then they have to pay the "regular" price.

The initial price and duration applies to the first time that user is purchasing the plan. Renewals will use the regular price and duration of that plan.