so yea, Mirbig, as mrgold suggested, check in the manual. but as i solved a similar problem before, my believe would be. only way to change permeability is by means of void ratio in stress/fluid analysis as both of them depend on each other in the equations. The other ugly solution would be to change the material, my means of removing the set, and add another set with same geometry and different properties. sounds like an easy solution but i tried it before and for me it wasn't very trivial.