Bug i've encountered on vanilla BG2 (no mod whatsoever, haven't found it on the forums so it might not be an issue anymore. Still... better safe then sorry)
Current behavior : upon exporting a mage character with familiar, you keep the extra life but the game doesn't remember you have casted the find familiar spell. Thus, in a new game if you are the main player, you can gain additional HP again, and again.
Expected behavior : I propose two solutions
1) upon exporting, the game should remember whether the mage had a familiar, or not. If the answer is yes, the next time he summons one it in another game, there will be no additional HP.
2) upon exporting, if the mage have a familiar, export the HP minus the familiar gain. (seems more easy to me)