More AI opponents in Local server game?

Is this a thing yet? possible to do? If so can someone please explain what method somebody would go about doing this?

Look at the section on "Configuring Planetary Annihilation" in the Dedicated Server Setup guide at eXodus.

Any way to do it without setting up your own server?

Install unlimited players and do the modification to the server directly to your installation of your PA, then play local.

You already have your own server on your PC, just modify the local files.

Install PAMM

Keep in mind that the AI can still use a lot more resources on the server than a normal player, so it might slow down a lot.