I don't remember seeing that rule.
I don't remember seeing that rule.
Which, about 3.5 allowing you to suppress effects, or abilities such as Frost requiring activation?
As far as I can see, Azhrei is correct. Brilliant Energy is always on, so you need to have a spare weapon if you want to kill undead or constructs, or sunder stuff.
As for activation...
Activation: Usually a character benefits from a magic weapon in the same way a character benefits from a mundane weapon—by attacking with it. If a weapon has a special ability that the user needs to activate, then the user usually needs to utter a command word (a standard action). A character can activate the special abilities of 50 pieces of ammunition at the same time, assuming each piece has identical abilities.
And then one of the energy damage abilities:
Flaming: Upon command, a flaming weapon is sheathed in fire that deals an extra 1d6 points of fire damage on a successful hit. The fire does not harm the wielder. The effect remains until another command is given.
Italics mine. Note that I believe it's been stated by designers somewhere that you don't need to deactivate the weapon property to safely sheathe it, since it can't harm the wielder (or by extension, their gear). So you can activate the Flame/Frost/Corrosive/Shock effect when you first get the weapon, and leave it on until you need to turn it off for whatever reason.