Sounds like you're overthinking it. You could just adjust your contributions (what amount from your paycheck goes to which funds) with your new money. Since you're still accumulating, and you aren't intentionally market timing, it's OK if your AA gets off by a few percent here and there.
Also, if you have TSP matching, you're screwing yourself out of matching funds by maxing out early. Some federal jobs give you up to 5% matching of your salary, but only if you contribute at least that amount on that paycheck.