This legacy is turning out to be loosely based on Pinstar's rules. I went ahead and started building an ugly house, but I'm still wondering what the game mechanics are to move a premade house onto an occupied lot, keeping the tenants intact.
I just tried this. I was curious if you needed the money available. If not, this method would be considered an unfair advantage and a cheat. But as it turns out, you do need to have the money available to afford the new premade house, just like when you start a new game. Houses don't have prices listed in the edit screen, so you'll have to know which your family can afford or you'll be repeating multiple times.
Method is similar in parts to moving the family to another neighborhood as described
here.
1. Enter edit town mode(
recommend saving the game).
2. Click the bulldoze button and select your lot. This will prompt you to evict the household. Choose the move out button. This sells the existing house and everything on the lot, except for what you stored in the family inventory and puts the family onto the clipboard in the upper left. This is temporary only! If you leave the edit screen or your computer crashes, the clipboard is lost. Good thing you saved the game before starting! Right? Right?
3. Click on the show empty houses tab at the bottom and choose a premade house. Click the place button and select your lot.
4. Click your family on the clipboard, choose place, click the lot with premade you created and click purchase.
5. Click return to game setup at the top, then click on choose a household at the bottom. Click your lot and then the select button. Then you're ready to play!