
zza ni |

the fighter can add one ability to the weapon as long as it has already a +1 (or that he also give it a +1 from his warrior spirit power along with the ability.)
i think the ability must still abide to the normal restriction of it's kind (so no keen on blunt only weapons or ranged ability on a melee only weapon etc. maybe also no holy and unholy on the same weapon..

MrCharisma |

Can you temporarily add a special ability using Warrior Spirit to a magic weapon that alread has a permanent one, e.g. add bane to a keen longsword +1?
Thanks.
Yup
Source Magic Tactics Toolbox pg. 10
The fighter can forge a spiritual bond with a weapon that belongs to the associated weapon group, allowing him to unlock the weapon’s potential. Each day, he designates one such weapon and gains a number of points of spiritual energy equal to 1 + his weapon training bonus. While wielding this weapon, he can spend 1 point of spiritual energy to grant the weapon an enhancement bonus equal to his weapon training bonus. Enhancement bonuses gained by this advanced weapon training option stack with those of the weapon, to a maximum of +5.The fighter can also imbue the weapon with any one weapon special ability with an equivalent enhancement bonus less than or equal to his maximum bonus by reducing the granted enhancement bonus by the amount of the equivalent enhancement bonus. The item must have an enhancement bonus of at least +1 (from the item itself or from warrior spirit) to gain a weapon special ability. In either case, these bonuses last for 1 minute.
So let's say you're a level 9 Fighter with Heavy Blades as your chosen weapon group, and you're holding a +1 Longsword.
You could add +2 to the weapon's Enhancement bonus
or you could add +1 and Bane to the weapon
or you could add +1 and Keen to the weapon
or you could add Holy (with no +1).
You could NOT add Bane and Keen together though, since the ability states that you choose "any one weapon special ability".
However if you were holding a +1 Keen Longsword then you could use this ability to add +1 and Bane, making it a +2 Keen, <something>-Bane Longsword.