Easily set smaller increment for 2nd month and beyond?

Hi,
Currently we’re paying writers for the first 30 days, for news posts this works fine bc old news gets very few views. However we’re working to build out a How To section with more evergreen visits. What I would like to do is to pay writers an initial payment + pay per view at rate 1, then after 30 days pay at rate 2.
I understand this is possible, by marking posts as paid, then changing the rate, then paying that rate for the previous month, then changing the rate back again for the new month. Then, add the smaller pay from previous months to the pay for the current month, back into time. So to be clear, the workflow would be:
1. All posts are marked paid
2. End of month, write down current month Writer Earnings, mark this month paid
3. Set view to last month, change increment value, write down earnings
4. Repeat for all applicable previous months
5. Add up all earnings, pay writers
6. Mark all months as paid, reset increment value.
7. Start over at the end of next month.
This seems like a lot of work and prone to mistakes.

What I would like to see (perhaps via plugin?) is a way to set two increments, one for current month, and one for previous months, and have the plugin(?) add up, calculate, and reset previous months all at once, with a provision for how far back in time to go (ie: 6 months). Until then, I will explore options, and not sure how much work this would be, except I do know that implementing a system as outlined above is going to be a lot of work, too 🙂