As a home owner through Habitat for Humanity I can not rent my home out while I still have a mortgage out on my home. When my mortgage is paid off in 25 years then that's fine. While that mortgage is still there the answer is no, not going to happen. Your home can be foreclosed on for that reason.
Can Habitat do that legally? Absolutely. At the end of the journey you go to the lawyers office and this is one of the things that is talked about.
Habitat built the house for you and no one else. To use the house in an opportunistic manner takes your right to the house away. I know that to some that may not seem right. Habitat builds for needy families living in substandard conditions, not for renters.
You are in a binding contract with Habitat to remain in that home until it is paid for. However, if something happens like the home owner passes away the house become an heir ship if there is no will. If you have a will it goes to who ever is on your will. Keep in mind how much you still owe on it and if the care and upkeep of the home can be realistically met.