I partially disagree with @Steve-Chambers:
You can cook them more, but it depends on how cooked they are already (if any) and what has been done to them before you got them. There is a point with most meats where cooking the for the wrong time leads to tough meat, but if you cook them longer, then the meat becomes tender - like pulled pork.
If they haven't been cooked already, I would brine, spice-rub, then slow roast or crock-pot/slow cooker for ~6-8h until very tender and meat falling off the bone. I would then sauce them using a sauce prepared for the occasion, which may be prepared from the juices from the cooking. Although having learned BBQ in Memphis TN, I also like a dry slow-smoked rib on occasion.
If the ribs have been cooked/smoked already, then cooking more won't toughen the meat too much so long as you can retain the moisture in the meat. I would reheat wrapped in foil in a slow oven (say 120 C/250 F) for ~30 min (size dependent) and then sauce with a heated sauce as desired.