No ty totiž máš sice v nadpise Javascript, ale jedná se o trochu odlišný unity javascript.

var texture1 : Texture2D;
var texture2 : Texture2D;
var alreadyUpdated = false;
var udelat;

function Update() {
    if (!alreadyUpdated && Input.GetKey(KeyCode.X)) {
        alreadyUpdated = true;
        RenderSometing();
       InvokeRepeating("povolKlavesu", .01, 30.0);
    }
}

function RenderSometing() {
    yield WaitForSeconds(9);
    renderer.material.mainTexture = texture1;

    yield WaitForSeconds(9);
    renderer.material.mainTexture = texture2;
 
}

function povolKlavesu () {

   alreadyUpdated = false;

}