How do you edit base camps on sims 3?

You press control+shift+C. This will bring up a bar at the top of the screen in which you type "testingcheatsenabled true" exactly as shown, then press enter. Once you've done this, go to the base camp, hold down the shift button (if shift doesn't work, hold down ctrl and click...it's been a while since I've used this cheat) and click on the lot. This will bring up a few options. You will want to select either "build on this lot" or "buy on this lot" depending on what it is you want to do