Re-enable settings ServerMapNameOverride from advanced play settings for dedicated servers in play in editor (PIE) mode from c++ in unreal engine. It reuses the existing editor user setting ServerMapNameOverride from advanced settings for play mode and play settings in editor.

CustomGameInstance.cpp

// Add module "UnrealEd" to the PublicDependencyModuleNames in your module build rules.

// Example how to override map for dedicated servers in play in editor (PIE) mode and reuse the mentioned setting.
// Use a custom game instance and override method InitializeForPlayInEditor from UGameInstance.
FGameInstancePIEResult UDefaultGameInstance::InitializeForPlayInEditor(
    int32 PIEInstanceIndex,
    const FGameInstancePIEParameters& Params)
{
    FGameInstancePIEParameters NewParams = Params;

    // Re-enable editor user setting ServerMapNameOverride from advanced settings
    // for play mode and play settings in editor.
    if (Params.bRunAsDedicated)
    {
        FString ServerMapNameOverride;
        Params.EditorPlaySettings->GetServerMapNameOverride(ServerMapNameOverride);
        NewParams.OverrideMapURL = ServerMapNameOverride;
    }

    return Super::InitializeForPlayInEditor(PIEInstanceIndex, NewParams);
}