Here's what I would use:
[CREATURE:SCORPION_DESERT_GIANT]
[NAME:giant desert scorpion:giant desert scorpions:giant desert scorpion]
[TILE:'S'][COLOR:6:0:0]
[MODVALUE:10]
[LARGE_ROAMING]
[POPULATION_NUMBER:2:3]
[CLUSTER_NUMBER:1:2]
[DIFFICULTY:3]
[EXTRACT:giant desert scorpion venom:7:0:1]
[EXTRACT_VALUE:100]
[EXTRACT_PARALYZE]
[EXTRACT_ANTIDOTE:giant desert scorpion antivenin:7:0:0:100]
[NATURAL][PET_EXOTIC][TRAINABLE]
[PARALYZEIMMUNE]
[GENPOWER:4]
[BLOODTYPE:W][CHITIN]
[PETVALUE:2500]
[GRASSTRAMPLE:10]
[LARGE_PREDATOR][SAVAGE]
[CARNIVORE]
[NOPAIN][EXTRAVISION][NOSTUN][NOEMOTION][NOSKULL][NOBONES]
[BUILDINGDESTROYER:1]
[NOFEAR]
[PREFSTRING:enormous tails]
[BODY:SPIDER:2EYES:HEART:GUTS:BRAIN:TAIL:TAIL_STINGER:UPPERBODY_PINCERS]
[SIZE:10]
[MAXAGE:20:30]
[ATTACK:MAIN:BYTOKEN:TAIL_STINGER:sting:stings:1:6:PIERCE][SPECIALATTACK_INJECT_EXTRACT:50:100]
[ATTACK:MAIN:BYTYPE:GRASP:snatch:snatches:1:6:GORE][ATTACKFLAG_CANLATCH][ATTACKFLAG_WITH]
[CHILD:3][CHILDNAME:giant desert scorpling:giant desert scorplings]
[FAT:1]
[ALL_ACTIVE]
[BIOME:DESERT_BADLAND]
[BIOME:DESERT_ROCK]
[BIOME:DESERT_SAND]
[STANDARD_FLESH]
[HOMEOTHERM:10067]
This means that they will appear more frequently and in larger numbers. They will also be able to reproduce and be trained for war-this defeats the purpose of leaving some untamed because war animals are more aggressive as well as doing double damage. You could add some dmblock or size if you wanted them to be even more powerful.
None of these changes require a new world.