My pediatrician told me to have two breast feeding boxes or bags of special things that only come out when I'm feeding the baby. I had books, puzzles, trains, play tools, etc. in the boxes and they'd come out when I was feeding. With newborns, you feed every two hours initially but then the stretches between get longer. But when you are getting ready to feed the baby, get out the box of toys that he hasn't seen for a few hours. Great for distracting.
I also did this--- again a suggestion from my wise pediatrician. I would say loudly to the baby "just a minute baby. I have to take care of X (his brother) right now. You have to wait." Now, sometimes the newborn was sleeping or sitting in a bouncy and obviously didn't know what I was saying or doing. It wasn't for his benefit that I said it. Instead, it helped my older son feel like I was being fair. Because the older kids are often told, just a minute when there is a new baby. So if I say it to the baby and older son feels like he is getting that attention, then when I say "just a minute" to older son for the baby, he is more prone to do it.
I would try to feed your baby in an enclosed room. We had a family room with a door and that's where I'd feed the baby . . . with the door closed. So my toddler couldn't 'escape'. Then he could do whatever in the room. I picked my battles and overlooked some things if they weren't that big of a deal. Sometimes if he is trying to get your attention by doing a million naughty things, ignoring it a bit will get him to stop taking that route.
good luck
It seems that your child is craving for attention which is quite normal when there is a new member of the family. What he needs is assurance that nothing has changed and that you love him as much as before. And explain to him that the little one needs more attention now as he is still very little, just as he was before. And tell him that you did exactly the same with him when he was a baby.
It will also be a good idea to get him involve in taking care of the baby such as asking him to get a diaper or anything for the baby and praise him when he does that.
Does your little guy tend to misbehave more when you are breastfeeding and can't pay attention to him?
If you were to tell your son to go to the corner to take a timeout, would he go to the corner on his own or would he be defiant?