Generating a Rift

1. Collect the Undaunted Developer Book behind Vigrod's tent.
2. Travel to an Interior cell you wish to clone.
3. Use the power learnt from the book. Undaunted will scan the cell and export all references to \My Games\Skyrim Special Edition\SKSE\UndauntedRift.pas in SSE Edit script format.
4. Edit the UndauntedRift.pas so line 5 contains the name of the cell you want to create and place it in your SSE Edit Edit Scripts folder:

SetElementEditValues(cell, 'EDID', '01_Undaunted_DwemerRuins01');

5. Load SSE Edit and run the script on any cell in the target ESP. This tool is not limited to just adding to the Undaunted.esp.
6. A new cell will be added to the ESP. Save the result.

Undaunted Optional steps:

7. Load the cell in the Creation Kit. Add a 01_Undaunted_RiftEnteranceMarker where you want the player to start the rift.
8. Place as many 01_Undaunted_RiftBattleMarker in the instance as you want. Each will spawn a Rift marked Bounty from undaunted.
9. Place a 1_Undaunted_RiftExit fot the exit.
10. Select the ground statics and build a Navmesh.
11. Delete the Room markers. Could do proper portals etc but this game is 9 years old.