Ok, so to close this problem, I finally solved it by using C++, by extending the Character class and reparenting my BP Character class to the new C++ extended Character class, to which I only added the GetAimOffsets function from ShooterGame’s character class.
The code for it is(in MyCharacter2.cpp):
FRotator AMyCharacter2::GetAimOffsets() const
const FVector AimDirWS = GetBaseAimRotation().Vector();
const FVector AimDirLS = ActorToWorld().InverseTransformVectorNoScale(AimDirWS);
const FRotator AimRotLS = AimDirLS.Rotation();
and in MyCharacter2.h:
UFUNCTION(BlueprintCallable, Category = "Game|Weapon")
FRotator GetAimOffsets() const;
so that I can use it as a node.
And now everything works as it should: