With PerfectworldDF you can set the sea level at a different height to get more or less land. Is there a way to do that with just DF's world generation settings?
Afaik that utility isn't doing anything 'special' in the sense of using values out of bounds or invalid values.
As such, it's just setting values that anyone can set via the Preset Field Values (p) interface in the Advanced Worldgen interface.
However, getting more or less ocean or land is pretty straightforward in default/vanilla DF.
Using this worldgen as an example..
worldgen
[WORLD_GEN]
[TITLE:LAND_WATER]
[DIM:17:17]
[EMBARK_POINTS:0]
[END_YEAR:200]
[BEAST_END_YEAR:200:-1]
[REVEAL_ALL_HISTORY:0]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:1:200:0:0]
[RAINFALL:0:0:0:0]
[TEMPERATURE:65:65:0:0]
[DRAINAGE:100:100:0:0]
[VOLCANISM:0:0:0:0]
[SAVAGERY:0:0:0:0]
[ELEVATION_FREQUENCY:2:1:0:0:0:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[POLE:NONE]
[MINERAL_SCARCITY:100]
[MEGABEAST_CAP:0]
[SEMIMEGABEAST_CAP:0]
[TITAN_NUMBER:0]
[TITAN_ATTACK_TRIGGER:0:0:0]
[DEMON_NUMBER:0]
[NIGHT_TROLL_NUMBER:0]
[BOGEYMAN_NUMBER:0]
[NIGHTMARE_NUMBER:0]
[VAMPIRE_NUMBER:0]
[WEREBEAST_NUMBER:0]
[WEREBEAST_ATTACK_TRIGGER:0:0:0]
[SECRET_NUMBER:0]
[REGIONAL_INTERACTION_NUMBER:0]
[DISTURBANCE_INTERACTION_NUMBER:0]
[EVIL_CLOUD_NUMBER:0]
[EVIL_RAIN_NUMBER:0]
[GENERATE_DIVINE_MATERIALS:0]
[ALLOW_DIVINATION:0]
[ALLOW_DEMONIC_EXPERIMENTS:0]
[ALLOW_NECROMANCER_EXPERIMENTS:0]
[ALLOW_NECROMANCER_LIEUTENANTS:0]
[ALLOW_NECROMANCER_GHOULS:0]
[ALLOW_NECROMANCER_SUMMONS:0]
[GOOD_SQ_COUNTS:0:0:0]
[EVIL_SQ_COUNTS:0:0:0]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:0]
[RIVER_MINS:0:0]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:0]
[SUBREGION_MAX:5000]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:100]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:0]
[CAVERN_LAYER_WATER_MIN:25]
[CAVERN_LAYER_WATER_MAX:25]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:0]
[LEVELS_ABOVE_GROUND:8]
[LEVELS_ABOVE_LAYER_1:8]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:1]
[CAVE_MAX_SIZE:1]
[MOUNTAIN_CAVE_MIN:0]
[NON_MOUNTAIN_CAVE_MIN:0]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:0]
[TOTAL_CIV_POPULATION:0]
[SITE_CAP:0]
[PLAYABLE_CIVILIZATION_REQUIRED:0]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
And looking at this line in particular:
[ELEVATION_FREQUENCY:2:1:0:0:0:1]
which is modified in the Advanced Worldgen interface via these 6 lines:
You can adjust how much land/water is generated very easily.
If you set the 0-20 Elevation Weighted Range to 2, and leave the Elevation Weighted Range (80-100) at 1, you'll get more water.
If you leave the 0-20 Elevation Weighted Range to 1, and set the Elevation Weighted Range (80-100) to 2, you'll get more land.
Beyond that, it's just whatever limits you want to impose on the world elevation.
If you don't have any elevation values below 100, you won't get any oceans. But you can get lakes.
If you don't have any elevation values above 99, you won't get any land.
If you take that worldgen above and generate it a few times,
typically (although not every time) you'll see roughly the same amount of land as water. Not always, but
typically.
If you use the 2/1 or 1/2 Weighted ranges, you'll
typically see more ocean than land, and more land than ocean. Again,
typically.
If any of the above is unclear, just say so, and I'll be happy to elaborate further based on what I've learned using the DF advanced worldgen interface.