Yes, you can do this. It is important to note however that inside of lines, the sides of a this quadrilateral are better described as segments. A quadrilateral has four sides, and if there are two sets of parallel sides, it is a parallelogram. A rectangle is a parallelogram, but it has four right angles. If you take a rectangle, and change the angles, you will still have a parallelogram that is no longer a rectangle. It will have two sets of parallel sides, but no right angles. Opposite angles will be congruent.