the connected property always reflects the actual state and is not changeable. To allow another player to get the slot, the old one has to be removed from the game. For slots where no player is not connected yet, it is possible to use VPlayMultiplayer::disablePlayer() or enablePlayer().
You can also add custom logic to your game, to e.g. introduce a temporary “removed/left” state for a player which you can handle on your own, and which has nothing to do with actual connected state.