This is something related to the original interface of the Kilobot. The ARGoS model mimicks what the Kilobot originally offers.
The function rand_hard() is implemented with a Mersenne-Twister random number generator that returns a 32 random bits.
It is not possible to change the range, but you can scale the values and add/subtract numbers to achieve the range you need. Refer to the
rand() Linux function for possible examples, as its logic is similar to rand_hard().
I made ARGoS.