https://forums.unrealengine.com/t/how-to-create-an-automatic-cast-conversion-node-for-custom-data-types-using-blueprint-libraries-in-c/775380

//.h
UCLASS()
class UMyAwesomeFunctionLibrary : public UBlueprintFunctionLibrary
{
	GENERATED_BODY()
public:
	UFUNCTION(BlueprintPure,meta = (DisplayName = "Convert To String",CompactNodeTitle = "->",BlueprintAutocast),Category = MyPrintableStruct)
	static FString Conv_MyPrintableStructToString(MyPrintableStruct);
};
 
//.cpp
FString UMyAwesomeFunctionLibrary::Conv_MyPrintableStuctToString(MyCustomStruct Struct) 
{
	return Struct.MyStringThatILike + " - " + FString::FromInt(Struct.FirstValue);
}