It is possible to reduce global sea level via filling empty lowlands with ocean water?
Based on calculations of the effect of melting ice on sea level, we know that to effect a 1 mm change in global sea level requires around 360 km3 water. The largest lake by volume, Lake Baikal, contains just under 24,000 km3 of water. So if you created an equivalent lake you would lower sea level by 66 mm. At current rates of global sea level rise that would offset less than 20 years of melting ice and thermal expansion.