It's not really a custom, just an adaptation of a new piece of equipment to go with an earlier item, but it seemed to fit here better than anywhere else.
On holiday in Malta, I bought the 4825 fire brigade accessory set, largely for the new hydrant but also out of interest to see the demountable hose reel. Having soft hose mounted on the rear of a fire engine is something only found on the European continent, mainly (I think) in France and Germany.
A bit of experimenting showed that the new hose reel system would just slip over the towing hook of the old style fire engine while the hydrant and the hydrant key will fit either side of the rear in the clips already on the chassis. Detaching and fitting the hose reel is a bit fiddly, but once on it looks a natural for the vehicle and it doesn't involve any modifications to my only one of this model. (I meant to buy oneor even two more while it was in the DS listing, but it vanished suddenly and quickly from the list recently.) Having the rear-mounted hose reel means that the tray with the two separate hose reels in which came with the original can be replaced by a storage chest to take hose fittings and other tools.