Couldn't you 'get away' with just a RCD fusebox DIN rail mount?
Technically you can do whatever you want.. (as long as its safe)
BUT
If the customer wont pay for your time modifying their wiring arrangements..
when all they want is a single faulty item replaced
e.g. Fused Spur with built in RCD - VS- re arrange fusebox to install RCD
it is a BUSINESS not a CHARITY that you are running!!!!
You could always replace an RCD socket with a normal socket or even put a plastic socket on a metal clad back box.
If a metal clad socket has been installed to provide additional mechanical protection in a garage/workshop enviromnet...
fitting a plastic item my leave risk of physical damage to that plastic fitting!
Even if you had a few spare MCB's and used these instead of a faulty RCBO for a day or two until you could get the correct parts?
Or don't I understand?
Which is the point I said at the start .. carry a few basic essential get you working bits..
then go back latter.. rather than trying to carry EVERYTHING to solve every problem on first visit!!
If you are trying to carry EVERY RCD type to do first time fix..
It can be very expensive option!!
Or looking at my call out last night..
customer rang 9:00pm.. Yesterday
By 10:30pm.. I'm back home after visit to site, temp fix, freezer back on.
By 1:30pm today.. Job all done, new RCD fused spur fitted tested all OK!!!
back home.. cash in back pocket!!!
eat me Sunday roast!!!
and a glass of Guiness Drink!!
Note:-
Brand new Y-Pages customer... chuffed to bits I turned out after 9:00 on Saturday!! (build the customer base for latter additional work!)