The problem Austria-Hungary faced had far more to do with leadership than manpower, although the quality of their troops is also relatively debatable. Suffice to say that much of the later struggles of the Austria-Hungary army could be tied to their early losses. The campaign in Galicia and losses at Lemberg, Gnila Lipa, and Rawa stripped the Austrian army of much of its most experienced officer corps, a loss from which it would never truly recover. To further augment the problem the Austrians had another problem, one of ethnic diversity. Their army employed large amounts of slavic troops and as these battles showed they were at best unreliable and at worst downright liabilities at times surrendering en masse to the Russians and even volunteering to fight against the Austrians.

To answer the question directly, had they relocated large quantities of troops from the Serbian front to the Russian front it likely would have made a difference in the early going, but later it wouldn't have mattered. As for replacing incompetent leaders with competent ones, well the problem was that Austria never had enough competent leaders to go around.