I can create P2P matches using EOSCore. However, when players are on same host that cause problem to connect. I made a test with changing/commenting +NetDriverDefinitions=…
Changing it before using a standalone game make it possible to connect two players on same host or I got this result for editor standalone games.
What is the way I do it without manually modifying the defaultengine.ini file?
Yes I have found it. You do not need to change the net driver. Now I did some modifications in DefaultEngine.ini (AndroidEngine.ini if needed for android)
Disabling NAT forces EOS to use direct connections between Players. Not trough EOS servers. Find [OnlineSubsystem] tag then add bIsUsingNAT=false line. Do this, then restart the engine.