Current Position?

Hello. I want to make a space shooter like asteroids (where the screen wraps around, so if the player hits an edge, they will go to another place). When I am using transform.position, how can I use the player’s current position for two values and have the other one be incorporated into a simple math function? So it would be something like this

transform.position = Vector3(Current X, Current Y, Current Z-30);

Thanks.

transform.position = Vector3(transform.position.x, transform.position.y, transform.position.z-30);

Though you could also IIRC:

transform.position += Vector3(0, 0, -30);

or

transform.position.z -= 30;