This exercise strikes me as most likely a waste of time and money.
LLMs can be used to whitewash a JD from a bad school, but you already have a degree from a good school. Other than that, LLMs are mostly for folks with academic ambitions. If you just want to learn more about tax law, you can do that the way you learn everything else on the job: read up. You won't learn how to be a deal lawyer in an LLM program - as you know, that just isn't what they teach in law school.
The MBA studies would be a little more useful, but here also I believe you will pick up what you need to know on the job. An MBA does look nice on the resume, but it doesn't make THAT much of a difference - certainly, IMO, not enough to justify taking a couple of years out of your career. And again, there is nothing stopping you from auditing a class or two on your own time, if you just want some exposure to MBA-think. Heck, these days a lot of schools publish recordings of their classes - I've been listening to podcasts of econ lectures in the car.
I know there can be a desire to collect degrees, but degrees don't pay the bills, and degrees mostly impress the people who aren't worth impressing.
Bottom line: you will learn transactional practice the same way you learned litigation practice: on the job. You need to find a firm or senior attorney willing to train you, and you will probably take a seniority hit in the short term as a result.
More importantly: As a transactional lawyer myself, I say welcome, and good luck. Life is better once you leave the dark side.