Rectangle {
    id: rect
    anchors {
        top: parent.top
        topMargin: Theme.paddingMedium
        horizontalCenter: parent.horizontalCenter
        //......other code
    }

MouseArea {
    //....other code
    onPressed: {
        rect.anchors.top = undefined
        rect.anchors.topMargin = undefined
        rect.anchors.horizontalCenter = undefined
    }
}