The overall balance stay the same , so yes you can use the same numbers 100PP above or down from a given PP the car was setting for.
The only parameters you have to pay attention , are :
Longitudinal grip : Acceleration LSD can be lowered to control sudden wheel spin on the external wheel , it can happen when you increase power.
Weight transfer above the 4 corners of the suspension: When you increase grip using softer tires compounds , you can increase springs stiffness , same amount on the 4 suspensions to contain mass transfer , avoiding the grip to pass over the tires.
You can also increase the Antiroll bars a few more points.
There also some exceptions off course. Normally on Maxed road cars using powerfull turbos increasing a lot the HP , you'll have to use some extremes settings to contain the car on his driving line. In this case , the normal medium powered car setting , will not able to contain the excess of power.
I hope i'll +- clear with this explanation..... not easy sometime to express myself in a clear way.