It depends how you have the functionality set up as to how easy it is. You totally can set up so that you use a multiplayer connection. There’s steam integration built into UE4. If you go to Edit > Plugings > Online Platform > Scroll down to Steam and enable it. Then go to your DefaultEngine.INI and get the steam integration set up with code from there.
Question though, when you talk about “Local Multiplayer” Are you talking LAN Connection? Or literally 2+ players on the same machine using controllers for inputs or something like so? If its local machine connections then yeah, you’ll have to do a lot of work, but I’m sure its possible, just set up some checks for that in the way you set up the matches.
https://docs.unrealengine.com/latest/INT/Videos/PLZlv_N0_O1gYqSlbGQVKsRg6fpxWndZqZ/index.html
I’m fairly new to Networking myself, I’ve been working through this as much as I can to get networking set up, and there are definitely ways of switching between a LAN connection and an Internet connection.
I’d need to know more information before actually giving any answers. However the tutorial I linked should hold some answers for you.