Based off the work of @zorz on their Sandbox Mod v10 Link
Upon further testing done I can see that it does not apply sandbox mode properly, limiting your ammo, I am working on a fix but it will take a while.
This mod adds extra maps to the Sandbox menu! Such as Flooded Lee, Raining Marina and Evertide Mall!
Instructions can be found in the included ReadMe file or read below. This if fully compatible with UMF and 0.5.2 and the Experimental Branch!
1. Backup your files, so that if things go wrong you can recover your progress
Do this by copying the folder "Documents\Teardown" and the game installation folder to a safe location so you can restore them later if need be. You can find the game installation folder from Steam: Right click the game > Properties > Local files > Browse local files
It is likely to be at this location, if you haven't selected a different steam folder:
C:\Program Files (x86)\Steam\steamapps\common\Teardown
2. Extract the contents of this zip into the Teardown installation folder and overwrite any files necessary.
This mod will overwrite following files(be sure to back these up first):
Additional files include images files to populate the sandbox menu:about.png flood.png frustrum.png hub.png mall.png Tstrom.png
3. Launch Teardown, open the "Sandbox" menu and Enjoy.
Alarms, fire alarms and timers are disabled in the Sandbox mode, so you're free to spend as much time as you'd like in the area.