Yes, it can be done.
However... By the time you do your first "port", you could have easily sold your current phone (and donor) and earned enough money flipping burgers to buy a better phone meant for that carrier.
It's not exactly easy, or fast and even if you manage (many fail) it without locking out your account (semi-common) or bricking the phone (also semi common), there is still the legal aspects. In some states it's blatantly illegal, period, end of discussion. In terms of federal law, it's a gray area depending on your intent and how good your lawyer is. All it takes a traffic stop to have a cop check, and yes some do.
It used to be worth it before Virgin and Boost got good phones, but not anymore. Unless you are a serious, but cheap, power user with skills, there is really no point in it.
As someone who has done it, my advice is to sell it and buy a phone meant for Boost. It's less time, less hassle, less risk and not only do you get support, but you get a warranty instead of voiding one.