I have the opportunity to buy a never used emergency slide from an Airbus A320 for cheap. So I need to know how they can be reused and how to deflate and repack them so I can use it for another time.
These slides may contain explosive squibs and/or chemicals not safe for ingestion and it is NOT SAFE to mess with them if you do not know what you are doing! If an airbag in a car can kill or cause injury, imagine an enormous version of that. If one became available for sale, I would be very cautious as to whether it had been made safe/inert. Tread carefully.
Only authorised life support fitter type maintainers at the factory or the approved delegated authority will be able to fold slides up again to the correct standard. It is a specialist type job and a jigsaw puzzle. It is similar to trying to get a tent back in it's bag if you don't use the correct technique.
As with all aircraft maintenance tasks, it may sound like a cop out, but the answer to any how do you do that question is "in accordance with the approved procedure". Find the approved procedure and you will know. It will be in the airbus manual or from the manufacturer of the slide.
The slide is just a slide and can be packed and inflated without pyrotechnics.
We use slides for training; we use them on the ground to demonstrate them as rafts, and to side down.
Manufacturer documents are used to maintain the slide, and will include packing instructions.
The slides are not hazardous to handle, neither to inflate nor repack. The exception would be if the slide is armed with the rapid inflator; that's something that should be handled appropriately. Otherwise, they can slowly be inflated.
For home use, I'd seek modification from a firm that does inflatable carnival or yard toys like a bounce house, that can bond a proper filler valve and make the slide usable for the longer term.
Be aware that aircraft slides aren't nearly as slick as one might think; going down a slide, you're quite likely to get friction burns on exposed skin, and I've burned a hole in uniform pants on them, as well as hurt my leg and hand.
If you're just using it for home entertainment, then inflating it and using it for bouncing, or things like that, are probably fine. I suppose it could be put on a lake, but they're not really meant for repeat use after that.