what is the effect of electrons in a penetrating orbital on Z* (the effective nuclear charge) felt by electrons in a second orbital?

Answer 1

The penetrating electron decreases the effective nuclear charge (increases the shielding) BUT not equal to 1 electron (because it just penetrates and doesn't stay in one place).

Answer 2

Not sure what you are asking but ... electrons in inner shells reduce the attraction between the (positive) nucleus and outer electron shells.