You could make the jumppad explode, but disabling it probably isn't possible with vQ3. You'd probably need to mod Q3 with a way of disabling triggers for a given set of time. What you could do is add an invisible door that moves over the jumppad, covering the trigger. For that to not be noticable, you'd need the trigger to be quite thin so that the invisible door can also be thin. It's an interesting idea though.
Exploding barrels will be func_button's with a health set to it. When you 'damage' it by a certain amount, it fires its targets, in this case one or more shooter_rocket's located inside the button and pointing towards the ground. The button will have a very fast speed so you don't see it moving, but just disapearing/reappearing. It'll also have a negative lip value so it hides itself under the ground. With a bit more innovation, you could make it show debri from the 'exploding barrel' for a short time after it explodes.