Yes, it can be fixed as long as the tissue is viable. It should be done by a vet with reptile experience. It doesn't necessarily need to be experience with chameleons specifically, but reptile experience is a must. In this case the bowel will need to be manually replaced very carefully and probably a suture (stitch) placed either through the side or over the vent to keep it in place for a while until it heals. This will require minor surgery. Some lizards do very well and are fixed the first time, and some have continued problems in the future. It depends on the individual lizard as to how well they will do. Now there is always the risk of it not going well, problems with anesthesia, or damage to the exposed tissue. So it's not a sure thing that it can be fixed, but he should definitely go to a vet for evaluation asap.
The important things right now is to keep it clean and very moist so the tissue does not dry out. I would place him in a temporary cage without branches immediately if he looks like he is dragging it or trying to rub it as you do not want this tissue to get damaged. If the tissue dries out it could die or become infected, which is not fixable and it would mean the end of your chameleon. KY jelly and warm sugar water to keep it moist until you can get it to the vet. If you want to take him to an emergency vet tonight call them first and make sure they are comfortable fixing a rectal prolapse in a chameleon. If they aren't keep it moist overnight and start calling around very first thing in the morning. Time is of the essence here.
Even if it cannot be fixed, or you don't want to put him through surgery for whatever reason, you still need to take him to the vet for humane euthanasia. It would be cruel and very painful to just wait for him to die in this condition. He should be fixed or euthanized.
Edit: It could be a rectal prolapse, or actually the hemipenes prolapsed and just very edematous and swollen. If it's the hemipenes those can be amputated fairly easily with no future adverse effects to your cham. Looking at the picture more it's a little hard to tell. Does it look like there is one tissue blob or two? Same advice still applies regardless.