A Game Piece with this trait will have a menu command that replace this piece with a different piece. You can select any existing piece for the replacement or define a new one from scratch.
Horizontal offset: The replacement will be placed this many pixels to the right of the original piece.
Vertical offset: The replacement will be placed this many pixels above the original piece.
Match Current State: If selected, VASSAL will attempt to put the replacement piece in the same state as the original piece. Layers will be set to the same level, labels will be given the same value, rotation angles will match, etc. The state of a particular trait will carry over only if it has an exact match in the replacement, i.e. the properties settings of that trait are the same in both the original and replacement piece.
Only match states above this trait: If selected, VASSAL will only replace states in traits that occur above this one in the list traits in the game piece editor. For example, the state of a Marker that's above this one will change if the state in the new game piece. If it's below, then it will not change if the new game piece has the same marker property.
EXAMPLE: A unit that can be destroyed but still leaves a wreck behind can be given this trait to turn it into a wreck. This is more convenient than dragging a new piece from the Game Piece Palette and can't be accidentally undone, as a Layer trait could.