Halfswording (grabbing the blade of your sword for more leverage to block a heavy blow or to thrust more effectively in close quarters with a longer blade) is a historically accurate technique in actual sword fighting. I've been told by friends that this is an invalid move in Bel and will result in losing the hand that grips the blade. I've checked the rules and can't find anything either in favor or against it. Has there been a ruling on this in the past? Is there a precedent that says one way or the other?

Halfswording is legal while the weapon is uncontested. A contested weapon is considered to belong to neither combatant, so if your opponent grabbed your handle and tried to take your weapon you would not be able to grab the blade at that point.