My personal opinion: I think it is possible, it needs some training and it has to "click". But also my personal experience is that over time it gets quite tiresome. It can work in a way that it does not harm passability too much, but people may still occasionally think it is strange. My base average pitch is about 110Hz, which is at the lower end of the male range, probably bass or close to it. My voice is now mostly neutral, so with visible appearance I can shift the perception towards female and on the phone I tend to increase pitch for some seconds initially to give the first impression. But I am getting tired of this, I still need voice therapy, using that changed voice for 15 years damaged it. Thats why I do after all consider surgery. But it is possible to do it without, it just is more work and needs constant care and good professional training to not damage the voice in the long run.
