How to setup my 26er MTB for indoor MTB park
Convert it to a single speed and slam the seatpost. Those will be the biggest things. Add a bash guard up front too for when your rear wheel falls off the teeter-totters and skinnies. 

A shorter stem would be a good addition too. It'll improve the steering for those technical sections. 

You might also consider a rigid fork. Suspension isn't really necessary for that type of stuff and can actually be a hindrance. That's why trials and bmx bikes have rigid forks. Surly makes a suspension corrected fork. Even with the correction, your front end will sit a bit lower than it does now, but you get used to it. 

You might want rim brakes too (if your bike is set up for either) for the same reason that you'll want a bash guard. You only have to land on a brake rotor once to really mess it up. You can true them to a certain degree, but they're never the same. 

If you stick with the disc brakes, you could try smaller wheels. 24" perhaps. But if you're going to go that far it's probably a better investment to just sell it (since you haven't been using it anyway) and buy a bike that's built for that type of riding. 

In fact, if you're going to be riding at this park more than once in a blue moon, you'd probably be happier doing that anyway.