I share your curiosity, so I asked my endo about this a while ago. He's very experienced in trans medicine.
He said that he keeps estrogen levels the same before and after surgery. Spiro is dropped of course, unless you're one of the few that have problems with T post-op; he then prescribes a greatly reduced the dose for up to a year.
I also asked about levels as you get older, past 50, and he also keeps that same. I was most happy to hear that one!