I'm guessing you would use the same minimap dot method as team capes that make the dot blue, but instead if a certain boolean is true, it won't update.
Same goes for player updating appearance. Simply make it so if the player has something on, it won't update their character.
public boolean undercover;
if (playerCommand.equalsIgnoreCase("undercover")) {
if (c.undercover == true)
undercover = false;
if (c.undercover == false)
undercover = true;
}