It really depends on what you like. You don't have the act of messing when you put a replacement in there. But you can stay longer in a full diaper. Sure it has its pros and cons.
However I prefer the natural way.
I couldn't imagine putting something that didn't come out of my body into my diaper. I know the feeling of messing yourself can vary from liberating to total shame, I can see why you would use pudding to simulate the feeling, squishy and mushy like a runny poop and unlike poop no bad smell. I'm just not sure how pudding would react to your skin. Use a lot of diaper rash cream beforehand!
Usually I don’t put anything in my diaper except what i produce... which happens to be poop and pee. Only because it’s so warm and thick diapers keep it warm for a little while. No matter what mess I’ve made though I feel icky so I quickly clean up and a fresh baby powered dry diaper is the best really.