The Mini will happily use HP or LP. Removing an HP air bottle from the ASA can be difficult due the to higher pressure.
You can add either a thread-saver, which screws on to the ASA to gas & de-gas the marker, or buy the regulator for the Empire Axe which incorporates a lever on the underside to do the same.
I use an NDZ thread-saver (from America for @£30). With a little silicon lube on the threads, the air bottle is very easy to remove from the marker.