If Pearl Harbor's radar warning had been heeded

How much changes if the radar warning at Pearl Harbor is taken seriously and U.S. fighters launch?

The first Japanese wave suffers much heavier losses because Hawaii had enough fighters to contest the attack if they were airborne in time.

The radar contact mattered only if commanders converted it into timely action. Hawaii contained a substantial fighter force, and getting enough of those aircraft airborne would let them engage the first wave before it struck unopposed. The attack would become much more painful for Japan, although the brief answer does not claim that every later consequence becomes fixed.