http://www.ufe3d.com/doku.php/code
A custom script could probably work
Prehaps OnRoundBegins would help here.

What I reccomend doing, is putting all your assets your want in that stage, and enable/disable objects at the start of the round depending on the current round.
1. put all your objects for your each stage version into a single scene or prefab.
2. For each object in the stage that you want to change based on round, parent them to empty objects based on the round they appear in.
3. Create an empty gameobject, and a new script. I will refer to this script as "stageRoundManager".
4. in stageRoundManager, create a gameobject array, and put all your round based props in the array.
5. in your script, subscribe to ufe OnRoundBegins.
6. In OnRoundBegins, write a foreach loop that will disable all your round based prop objects. Then, enable the round based prop objects with the index of (roundNumber-1).
7. Don't forget to delete the unused update and start functions, and unsubscribing to the event with the onDisabled function.