I had a lot of trouble finding documentation for how to set the refinement level for an object with the CollisionAPI. The following code should do the trick.
from pxr import Sdf
prim = prims_utils.get_prim_at_path("/some/prim/path")
ref_level = prim.GetAttribute("refinementLevel").Get()
if ref_level == None:
prim.CreateAttribute("refinementLevel", Sdf.ValueTypeNames.Int)
print(prim.GetAttribute("refinementLevel").Set(2))