I think that first “Single Player” was supposed to say “Multiplayer” … if not, then I am very confused.
The easiest solution is probably to not distinguish between Single Player and Multiplayer. In either case, create a dedicated server and connect to it and all the code will work the same.
This does make me wonder though … if you have a Singleplayer game without a dedicated server and you execute RPCs and replication, will it still work? It would be a little funky as your client would effectively just be talking to itself but it would allow you to code for multiplayer and still have it work for singleplayer (without a server).