From Scale around points similar to rotate around

    public static void ScaleAround(Transform target, Vector3 pivot, Vector3 newScale)
    {
        Vector3 A = target.localPosition;
        Vector3 B = pivot;

        Vector3 C = A - B; // diff from object pivot to desired pivot/origin

        float RS = newScale.x / target.localScale.x; // relative scale factor

        // calc final position post-scale
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        Vector3 FP = B + C * RS;

        // finally, actually perform the scale/translation
        target.localScale = newScale;
        target.localPosition = FP;
    }