| Pharazon |
I can't think of a rule off hand that would make it increase the CR. The bestiary is using an average HP total but like with players you will have some above and below that number. I alter my monsters slightly anyway so the players who know the bestiary well are kept guessing a bit.
I would also think that so long as you are maxing the hp on the players that maxing the health on the monsters would be a fair trade even though I dont think you even have to worry about that really.
--Pharazon