You are assuming that we can alter our speed, which isn't true. Our speed through spacetime is c. If you are at a fixed point in X,Y,Z, then your velocity is c

You are assuming that we can alter our speed, which isn't true. Our speed through spacetime is c. If you are at a fixed point in X,Y,Z, then your velocity is c in the direction of time. You can change _direction_ in spacetime, but you can't change your speed. If you set your velocity to [1,1,1,x], then x (your speed in time) MUST be sqrt(c^2-3). And still, once you've done that, you cannot "scale your velocity", because you cannot change your speed. We can only change direction.