Not exactly sure of the question, but if you're in the Crop window in Lightroom's Develop module, there's a little 'lock' icon in the right panel beside 'Aspect'. If it's locked, LR will scale but won't change the aspect ratio. If you click it to unlock it, then you can set any aspect ratio you want. You can also play around with what happens when you hold down the Shift or Alt/Opt key and move one of the control points.
Mike.