I have been in a pretty hard situation where my only chance of beating a chief is having an ability which I cannot "buy" using points as I have spent all of them. So, in order not to load a previous save, is there any Godmode cheat to enable and pass that obstacle?

Thanks in advance!

There may be other areas you can explore first. Even at the beginning of the game you can leave Aleroth and level up outside (the orcs are vulnerable to poison, if available, and the ones to the west, north and east are weaker and in smaller groups than the ones if you head south). Don't forget about the catacombs, though; certain main plot quests will trigger the quests in Aleroth to finish on their own, if they are not done by then, causing you to miss the rewards.

There is a save editor and item editor you could use to edit your character or give bonuses to an item to use temporarily.

Enough restoration potions should get you through any fight where you can not be killed in a couple hits. Early in the game individual health potions are more effective, but the same holds true (you'd just need to use an exploit to get unlimited potions).

If you do a round of checking merchants, you may be able to find equipment upgrades or spell books for sale (or if you are still in Aleroth, at least more potions). Quicksave before talking to or mousing over an NPC (or hitting Alt), and you can trade, then reload to try again if they don't have anything. NPC inventories reset about every 10 or 15 minutes real time (depending on the NPC).
I found a Burning Wall spell book randomly in Mardaneus' house my first game, which was the only way I could defeat the giant spider at the bottom of the catacombs. It also came in handy for the first strong orc you meet heading south of Aleroth, but I never used it again after that (playing a warrior).
Depending on how far you are in the game, Kistandalius or (to a lesser extent) Blake in Ars Magicana and Corinna or (also to a lesser extent) Mpenzak in Verdistis are some of the better NPCs for getting spell books.

Share your monster killin' tricks

Chasing Josie... techniques for defeating Josephine

Thanks a lot again Raze, helpful as always! Last encounter with Josephine in Black Lake Dungeon is the one which keeps me in trouble as I have not hellspikes. Will try some of the solutions you and other lads provide in your last link you posted. Be well!

Josephine starts with a summon and casts a spell on it, so if you interrupt that (say by whacking her with a sword; having the passive Stun skill helps) she will keep trying to summon, and not switch to Hell Spikes. Depending on your hit points, armour and number of restoration potions, you should also be able to walk over the Hell Spikes to get to her (as a warrior) or not be too bothered by them (with a ranger or mage). A shadow potion (or Fade From Sight, etc) could let you hide to heal and approach unnoticed, or otherwise position yourself, for an attack.

Shadow potion used once and swirl special attack did the trick easily. Thanks again!