Modeling with NOL

Building a PE model that involves net operating loss / tax loss carry forward. One part of this model is to show unelected IRR and it should stay the same regardless of any change in leverage. Am struggling with formulating unelected FCF or FCFF and how to remove the effect of leverage.

I tried to build an IF function to determine whether before and after tax income change signs, but still cannot figure out what to do for the year when NOL is exhausted.

Appreciate any insight here.