I have the same question as the above person. It appears from the forums out there that the player will just have an extra property. It does appear that you can pick a member of the household to make that 2nd property the home that character lives in. Once you've purchased a new home, you can chose to have the character have this as his/her main residence. I seem to recall that when that character is the one you have active on your dashboard, you click on the property bubble and chose the option to make the new home the primary residence. So with this method, you can have people living in two or more different places should you have multiple active Sims. I am thinking that you can assign a bed in the old place to your roomate (an NPC that you've invited to be a roommate), but have yet to try it. To EA: Renting out your old home or one that you've built does should like a great 'self-employed' option. It should be added just like the 'writer' and others.
I am sorry you received the last response that (I'll paraphrase) - I don't know, post your question elsewhere. I am sorry that person wasted your time.