First answer,, u will need tomes,, tome of health, or something like that,, Or make a custom tome, but remove the effect, it will increase life, but it wont show any tome-effects,,
Second answer,, i dont think so,, However, i once saw a nice (vJass or Jass) system that, i thought, could do that! I will search for it,, give me a sec,
Oh, and that system also included increasing life and so on,, i thougth,,
EDIT: Found it! It has 2 librarys,, So you need to use JNGP,,
This is vJass, but you dont have to edit ANYTHING about it, just use custom script to call the function you need,,
http://www.hiveworkshop.com/forums/f413/vjass-bonus-mod-setunitmaxstate-65622/
Bonus Mod library includes increasing damage,, SetUnitMaxState includes max life,,
RE-EDIT: You have to edit SOME things about it, some raw codes,, if you want i can implent it for you