I'd let it go.
But I'd be very tempted to put in the middle initial, quit next year as planned, and eagerly await the exit interview/why are you leaving question. Answer: "The environment in our office is too petty and doesn't support its designated team leaders. Even on issue as small as a middle initial, poor communication and no support. I felt disrespected and I have better options."
You sound like you want to use your upcoming freedom to light this fire. It's your life, you're free. Do what you want.
Personally I wouldn't want to die openly over this tiny issue because I feel the pettiness would reflect badly on me. I'd feel like the team lead version of Milton in Office Space with his stapler. This as a former accountant myself.
Hmm, there's a deeper point to consider. If you feel disrespected, it's possible that your subordinates do too. They are lower on the totem pole and, according to you, their immediate supervisor/team is "quite particular." Going over your head isn't considerate, but perhaps they are doing it because they feel overly controlled. If so, it's entirely possible that your own boss views both you and them as petty in this matter and wishes both sides would just drop this irrelevant matter. In this case, dropping it is wise as a preventive measure. Quitting or fighting hard over this issue is the kind of thing where boss-level and supervisor-level people will tell this story about you behind your back later - not maliciously, but sadly. It's the kind of thing that changes an informal referral from "detailed, technically skilled" to "picky...smart but petty, not good supervisor material." Did I mention that I'm a picky, detailed FORMER accountant??
But I'm not in that office feeling those feelings. You're the boss of you!
In any case, glad you have FU money.