Step one, open the world in legends mode
Step two, hit "p"
Step three go to you /Dwarf Fort 34.11 folder and open the region#-world_gen_param notepad and copynpaste (you can also put this in the world_gen folder in the init folder to make this a custom world, that way you can tweak the number of megabeasts and such.)
Here is a world that I came up with, sadly the evil lake is not filled with undeath (and if you add +1 volcanoes to the gen it becomes a good lake.) I'm looking for a spot for which I can minecart shotgun the corpses of invaders back at invaders in a reanimating biome.
[WORLD_GEN]
[TITLE:CREATE WORLD NOW = Mountain Lake]
[SEED:IUcauooeKK2oqKqwCAUO]
[HISTORY_SEED:aBQl4ttucxo2ErcW4IvN]
[NAME_SEED:1Wk636ulVB1a017O0clL]
[CREATURE_SEED:NcJT9FqJu5IQ35gEBA1x]
[DIM:65:65]
[EMBARK_POINTS:1524]
[END_YEAR:300]
[BEAST_END_YEAR:5:-1]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:600:100]
[RAINFALL:0:100:400:400]
[TEMPERATURE:10:75:101:400]
[DRAINAGE:10:100:500:500]
[VOLCANISM:0:100:600:600]
[SAVAGERY:0:100:200:200]
[ELEVATION_FREQUENCY:3:2:0:1:0:1]
[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:3:1:2:3:4:5]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[MINERAL_SCARCITY:800]
[MEGABEAST_CAP:200]
[SEMIMEGABEAST_CAP:300]
[TITAN_NUMBER:120]
[TITAN_ATTACK_TRIGGER:60:0:100000]
[DEMON_NUMBER:25]
[NIGHT_TROLL_NUMBER:11]
[BOGEYMAN_NUMBER:11]
[VAMPIRE_NUMBER:11]
[WEREBEAST_NUMBER:11]
[SECRET_NUMBER:10]
[REGIONAL_INTERACTION_NUMBER:22]
[DISTURBANCE_INTERACTION_NUMBER:22]
[EVIL_CLOUD_NUMBER:11]
[EVIL_RAIN_NUMBER:11]
[GOOD_SQ_COUNTS:60:40:0]
[EVIL_SQ_COUNTS:100:70:0]
[PEAK_NUMBER_MIN:10]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:3]
[VOLCANO_MIN:5]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:5:0:0]
[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:250]
[RIVER_MINS:5:5]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:75]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:25]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:5]
[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:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:4]
[NON_MOUNTAIN_CAVE_MIN:6]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:20]
[TOTAL_CIV_POPULATION:15000]
[SITE_CAP:510]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:136:272:136]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:528:1056]
[VOLCANISM_RANGES:0:0:0]