Board Thread:The Quarters - Q & A/@comment-26447681-20150530054133/@comment-24672610-20150530220345

I don't know of a way to make that happen automatically, but you could make a note of what your health is just before you level up, then use Fix Character Values to return your health to that value (or whatever value you want it to be if you're going with partial regeneration) after leveling up.

This may be preferable to the negative Habit idea in that it allows you to return your HP to the precise value that you want, and it won't reduce your mana as a Habit would.