If your Changing a CU then you must be taking responsibility for the circuits you reconnect, tecnically a PIR should be carried out on the instalation. its your responsibility to make sure that the circuits being reconected are safe. so a PIR and EIC would be needed.. I usually note on the EIC that the cert covers both therefore I normally put a LIM or N/V in the routing of cables box...
It's quite a common misconception that by issuing an EIC, for an addition or alteration, the issuer is taking responsibility for the existing installation.
This has never been the case, and the IET has taken steps to try to disuade people of this misconception.
The notes on the rear of the 16th and the 17th edition EIC model forms both indicate that EICs should only be used for initial certification and are not be used for PIRs.
Due to the number of people it was found were using LIM on EICs, an addition to the notes at the bottom of the 17th edition schedule of inspection model form was made, which states LIM is "applicable for a periodic inspection only."
In both editions, there is a box for comments on the existing installation, and both editions have a Regulation requiring that any defects or ommisions revealed during I&T, be made good before the Certificate is issued.
We now have the 17th 1st amendment, Which has introduced separate schedules for initial certification, and condition reports.
There is no reference to the term LIM in the model form schedule for initial certification. It is now only refered to in the schedule for a EICR.
We still have the note on the rear of the EIC informing us that the EIC is to be used only for initial certification, and not for a Periodic inspection.
We still have the box for comments on the existing installation.
And we still have the requirement not to issue a Certificate untill any defects or omissions revealed during I&T are made good.
By using an EIC to cover both initial and periodic certification, you would not be complying with BS7671.