This is a house-ruled version of the same spell from the core rules: http://paizo.com/PRD/spells/magicWeapon.html#magic-weapon-greater. The house-ruled portion has been italicized.
School: transmutation; Level cleric 4, paladin 3, sorcerer/wizard 3
Casting Time 1 standard action
Components V, S, M/DF (powdered lime and carbon)
Range close (25 ft. + 5 ft./2 levels)
Target one weapon or 50 projectiles (all of which must be together at the time of casting)
Duration 1 hour/level
Saving Throw Will negates (harmless, object); Spell Resistance yes (harmless, object)
This spell functions like magic weapon, except that it gives a weapon pluses to be assigned as an enhancement bonus on attack and damage rolls, or as other magic weapon properties. You gain one plus per four caster levels (maximum +5). This bonus does not allow a weapon to bypass damage reduction aside from magic.
Alternatively, you can affect as many as 50 arrows, bolts, or bullets. The projectiles must be of the same kind, and they have to be together (in the same quiver or other container). Projectiles, but not thrown weapons, lose their transmutation after they are used. Treat shuriken as projectiles, rather than as thrown weapons, for the purpose of this spell.
- Grant a weapon an enhancement bonus that does not stack with any existing enhancement bonus. Any other magical properties are unaffected.
- Imbue an existing magic weapon with effects upto that weapon's normal enhancement bonus. Effects granted from GMW suppress any effects the weapon normally has (other than its enhancement bonus) until the spell expires, is dispelled or is dismissed.
- Imbue any weapon with both an enhancement bonus and other effects. Any properties the weapon already has are suppressed until the spell ends. The bonuses due to effects cannot exceed the enhancement bonus given to the weapon. i.e. for a +5 bonus, You could imbue a weapon as a +3 holy weapon but not a +2 holy keen weapon.