Answer
There is no effect in either case.
Work Step by Step
$$Current = \frac{voltage}{resistance}$$
$$I = \frac{V}{R} = \frac{2 \; V}{2 \; R} = \frac{0.5\; V}{0.5 \; R} $$
If both voltage and resistance are changed by the same factor, the factor cancels out and the current is unchanged.
