Late reply, but I read that someone's making a trip in July in the thread, so might still be relevant.
I live in Sao Paulo, never been to Rio, however over here it's pretty bad if your appearance doesn't make people see you as a woman. Back when I was transitioning, in 2014, I got insulted in the middle of the street and in the subway many times (in broad daylight), as well as sexually harrassed. I've never been beaten up or anything, but from how everyone acted, it wouldn't be weird at all for it to happen, and nobody would help.
Even now, I often catch people staring at me with weird looks in the subway - I know how to recognize what look means what from what I've been through - and am still insulted sometimes, just much less often. That's with me "passing" though, and even if someone were to confront me, my voice is completely feminine so I'd at least be physically ok.
Sao Paulo is a relatively advanced city in comparison to the rest of Brazil, too. Rio's probably the same in regards to how people treat trans people. It's way worse in small cities and the northeast region (even in the metropolis).