You can't do that. Doesn't matter if you have a modified launcher, a server will never give you the position of a vanished player.Manthe, If you made a program to modify the client be for lunching minecraft, and make vape compatible with the changes then it might be possible.
Maybe if someone is using an invisibility potion or a poor vanish plugin but the classic vanish doesn't give away your position.Nope some client like serenity can say what player is in vanish and it work perfectly ( but it is a version client not a mods / injectable )
That doesn't tell you if you're being watched though.No it doesn't say the postion it just say what player is in vanish