If you want them to spawn normally, you can just add the Halloween event to your server/launch settings: -activeevent=FearEvolved

That will randomly spawn in all the other Halloween shiny dinos as well.

If you want just the Trick or Treat dinos to spawn, you can add them to the variant overrides in the Gameusersettings.ini. Under the [shiny] header, look for VariantWeightOverrides, and you can add it to the existing list of specialty shines: Trick-or-Treat:xx, with the xx being whatever frequency you'd prefer.

That will also allow you to spawn Trick or Treat dinos even during other events. However, they will always only convert to Halloween colors, like eldritch, pumpkin, ghoulish, etc. FYI, you can also add the Lovers shiny from the Valentine Day event this way.

If you'd like to bring them directly in, you'll need the admin gun, which you can only get via console: cheat GFI ShinyVariantGun 1 0 0. Then just find the dino you want to make a ToT (or just spawn one in) and rotate thru the gun settings until you get to Trick-or-Treat.

You might need to do the ini change in the previous step if it doesn't show up on the gun.