The team got a question today from a player asking if they could add duplicates of existing homes to their town. The answer is no. The intent of the following rule has always been that you can add missing lots. So, I italicized and clarified the following...
Creating Your Scoring Game File
All challenges begin in a fresh, virgin, completely unaltered town of your choosing. If you wish to place a missing EA lot such as the spa, then you must do so at the beginning of your file. Personal inventory items may be placed on non-home lots, but aside from this, non-home lots must remain unaltered. Unless a particular ruleset lays down restrictions, you are free to travel and/or move to any neighborhood or town. Options - all default settings: Autonomy > Full; Auto Age (Played Sims) > Yes; Auto Age (Unplayed Sims) > Yes; Sim Lifespan > Short; Seasons players > No Extreme weather. Do not start any holidays of your own and turn off any holidays on the calendar.