It seems to me that change in permeability should not shift the equilibrium of entering and exiting ions, except how fast equilibrium is reached. Consider this: two compartments are separated by a membrane. 1st compartment holds 1mM Na+ and 10mM K+ and 2nd one holds 10mM Na+ and 1mM K+. Let's make the membrane equally permeable to both species. Result: the species will become equally mixed on the two sides and the equilibrium potential reaches zero. Let's rewind and start over. This time let's make the permeability of Na+ half of that of K+. My prediction: there will be equal mixture of the two species on both sides ultimately, it will just take longer for it to happen than in the first scenario. Equilibrium potential = zero.