Correct answer: remains same
Since the original resultant is $R=P+Q$, we have $R-P=Q$. So the replaced force is $2(R-P)$ in the opposite direction of $Q$, which is equivalent to $2Q$ opposite to $Q$, i.e. $-2Q$. The new resultant is $P-2Q$, and using the given relation this simplifies to the same resultant as before.