Have you tried using the Step Sequencer? There is more to the SS than meets the eye at first glance, including the ability to randomize parameters for each loop created. It may also be easier to adjust notes, as the "first level" of interaction is simply turning the MIDI event on/off. The "finer details" is another level down into the GUI, but it seems the top level is what you are trying to achieve. You may find this simpler than trying to modify rhythm patterns in the PRV (I personally find the PRV painful for doing this).
You can access the SS in the upper right of a VST, and if you create a simple pattern you can right click that in the track view, convert to groove clip, and extend it as far as you like. There are a few nuances with working with the SS, but for quick modifications & ease of use (for your purpose), you may want to check that out.