No, you cannot change the sex of a plant. Actually you can't even turn a female male, but you can make a female grow male parts and the reverse is probably true. This is not a desirable thing however and you never want it to happen.
While I don't know if I would go so far as to advising new friends, but definitely do not listen to this person in regards to anything about growing as they are obviously oblivious.
I grew out Bodhi's headtrip. The male I chose for breeding threw out a few hairs. I posted a pix at breedbay, which is where Bodhi hangs his hat. Bodhi showed me his male, with exactly the same trait. The breeding I did was called the box of chocolate, and 4U2smoke was kind enough to test some of them. There was a single nanner that showed, and I suspect it was from using hermi's to breed with.
I think so. That info came from DJ Short in his book on breeding. From a purely genetic point of view, it is a crapshoot. You may or may not get a great offspring because cannabis being a diploid both parent provide 1\2 the genes, but there is no way of knowing which half either parent will donate.