Replacement consumer unit. Listed building consent ?

No. In any event, the problem is the home owner's and not yours.

True but, the home owner or their representative may need to spend the morning on the 'phone to the local council planning dept, who are the final arbitration, for normal listed private property; and he or she may need your technical back up to explain exactly what is being proposed.
Mike.

 Chris. I believe both the owner and contractor are responsible for damage to a listed building

https://www.buildingconservation.com/articles/dutyofcare/dutyofcare.htm#:~:text=can%20be%20sustained.-,',the%20IHBC%20Law%20&%20Practice%20Committee. 

Those carrying out works to historic buildings (be they owners, agents or contractors) need to reminded that unauthorised works, damage or failure to comply with a Listed Building Enforcement Notice is a criminal offence and can result in a fine of up to £20,000 per offence in the Magistrates Court with more serious sentences in the Crown Court, as well as having to meet the local authority’s costs.

I think it's also stated in the regulations (chat GPT certainly thinks so) but document was just too big to start trying to find the text.

 Chris. I believe both the owner and contractor are responsible for damage to a listed building

https://www.buildingconservation.com/articles/dutyofcare/dutyofcare.htm#:~:text=can%20be%20sustained.-,',the%20IHBC%20Law%20&%20Practice%20Committee. 

Those carrying out works to historic buildings (be they owners, agents or contractors) need to reminded that unauthorised works, damage or failure to comply with a Listed Building Enforcement Notice is a criminal offence and can result in a fine of up to £20,000 per offence in the Magistrates Court with more serious sentences in the Crown Court, as well as having to meet the local authority’s costs.

I think it's also stated in the regulations (chat GPT certainly thinks so) but document was just too big to start trying to find the text.

Alan B said:

Chris. I believe both the owner and contractor are responsible for damage to a listed building

True, but it is the owner who has to deal with the issue of obtaining consent.

I cannot see how a more or less like-for-like replacement of a CU would affect the character of a building, but installing an additional one might be a different matter.