Unit cost no, that refers to the type instead of a specific unit instance. Max life/mana can be modified with item abilities. There is an abusable bug with them. You can usually have multiple levels for abilities, but these specific abilities do not properly update when you set the level ingame. However, if you remove them from a higher level, this level's bonus is subtracted. Example:
lvl 1 --> 0 life
lvl 2 --> -10 life
Add the ability to the unit ingame, set it to lvl2 and remove it again. It will first gain the 0 bonus from lvl1, not update when switching to lvl2 and then subtract the -10 from lvl2, therefore resulting in +10 life permanently and without ability. So the bonus is cumulative.