Experimental Version
This version will let you go to 24 slots by default. The reason for this is to help limit performance issues on lower-end machines. However since it's not my place to decide where your limits are, you can indeed override this by adding "true" to the end of your command. Understand I am not responsible for any menu-related issues that come from using this version, as these are out of my control.
WARNING
The experimental version should be considered use at your own risk.
Once you go beyond 9 sims, you can no longer use Manage Household in that save as it may sometimes crash the game when trying to generate the portrait for 10+ households. This won't cause any damage other than loss of unsaved progress, but it should definitely be noted to avoid it when possible.
Workarounds:
These are game constraints and we unfortunately do not have access (at this time) to override them.
Create a Household: Click on a lot and select Create Household there instead.
Place Existing Household: Click on a lot and select Create Household. Then from CAS, load the household from the gallery/library.
Delete a Sim: Only 8 sims will show up in CAS. To delete extra sims, use the included tm.deletesim command.
Edit a Sim: You can not edit a sim while they're part of an extended household. Doing so will remove all but 8 sims.