Consumer units are essentially an array of dinrail mounted devices, forming the whole assembly.

While each item in the consumer unit is available as a separate item, and has it's own BSEN etc, a consumer unit as a whole is "type tested" as an assembly, and should be installed as per the instructions.

Mixing MCB manufacturers in a consumer unit often happens (some will fit others etc), but an electrician doing so breaks the "type testing" of the consumer unit.  I would assume that moving internal parts would do the same.

While I do not know of any events of an electrician falling foul of a change to the consumer unit in terms of manufacturer MCB or position of mains switch, altering it does go against the type testing of the item, and as such would not comply with BS7671.

In saying this, I have seen many MANY consumer units with mixed manufacturers, and with relocated internals.

I don't think there is a definitive yes/no.  Sorry