I thought the re-wire-able, cartridge, and MCB were all different with the Wylex fuse box? it is only one screw to change the base, but do make sure main isolator is off as live parts exposed.
Personally I would not change the fuse/MCB as once reduced in size, in the future you don't know if the size can be increased again.
Although my old house the Wylex fuse box was RCD protected,
this is unusual, also the old Wylex can only have over 32 amp in one slot which has reinforced contacts
and the main switch is limited to 60 amp
so at some point in the future your likely to want to change it for a modern consumer unit. It took me 6 months after I moved into this house, but the problem is without RCD protection although the regulations are not retrospective so existing things can continue to be used, at some point you will want some thing which means RCD's need to be fitted, new shower, new boiler, new socket, etc.
So it is just throwing money away buying some thing which will likely be scrapped in the not so distance future.