@Shadius No worries, when you combine networks, there is no change or impact to any configurations. It simply changes the way your menu locales appear in the Dashboard. It's purely administrative and nothing will change or reboot, no hiccups. 😁
You can create a few separate test networks and then combine them to try out the process first. Even creating a couple empty networks to test that is fine, but if you have some spare/lab gear like a switch and an AP or whatever, go ahead and add them to separate networks and have a live config running on it when you combine them, just to prove it out before you do it on the production network.