I really don't think you can discipline a child of that age because they don't understand cause and effect until closer to 3, so they're not really capable of making the kinds of connections they need for discipline to be an effective way of changing behaviour. Honestly, re-directing to more positive behaviour is the best method.
My kids are older, so I haven't been in the trenches with a toddler for a long time, but one of the things about parenting is being aware that as your child grows and develops, what worked as an effective strategy last month or week or yesterday, might not work today. I think he's trying to tell you that the playpen isn't working for him at this moment.
Pressing buttons and throwing things is part of learning about the world and the effect he can have on it. Obviously he needs to learn as time goes on that he can't walk around throwing everything. But for now, I press this button, it makes this noise, I throw something it makes a crashing sound and Mummy comes running, is the beginning of learning about cause and effect and it's part of him exploring the world.
He is the kind of baby that will not wind down himself.
But if he's in the playpen from 6-7 and then goes to bed, he is winding down himself.