Change Base Dmg &/or Armor Via Triggers On-The-Fly With No Abilities?

Is it possible to use triggers to just modify the base damage or armor of a unit mid game without using abilities to add to the unit?

No.

Create a spellbook based spell, disable it and put a modifier appropriate to the desired effect in the spellbook

No base damage and armor (the ones that are in white-colored text not green) can be changed/subtracted/added by any means without using Upgrades.

Upgrades are one-time use, once you set its level, they cannot be rolled back you only have to go straight on.

Base damage can be done by tomes.

He said with no abilites.

I'm sure he meant no bonus damage abilities (the ones that show with green plus numbers). Otherwise, he's being hopelessly optimistic.

Stil I'm almost sure there is no +armor tome anyways