Is there a way to control the set of values for cassandra-stress?

I am trying to test a cluster that has a set of tables with hexadecimal values.

Is there a way to instruct cassandra-stress to use hexadecimal values?

The current column spec (relevant section) looks like this:

columnspec:
  - name: enduser
    size: fixed(32)
    population: uniform(1..300000)
  - name: device
    size: fixed(32)
    population: uniform(1..20)
  - name: hash
    size: fixed(32)
    population: uniform(1..20)

I could not find a way to set columnspec to a set of characters, or control any way the value set for the population.