Any new circuits will come under part p, and adding additional CU will too, very little can be done as far as electrical installation is concern without it being covered by part p. This will also require Installation Certificates.
A new circuit from the consumer unit needs notifying under Part P.
The wiring regulations and Part P are separate documents.
As far as trying to twist the wording to suit what you want should anything go wrong it would be up to the courts to decide. In the past the courts have looked at what was intended not actual wording so you would not win.
Also there is the problem of insurance and selling the property later.
So to be legal the work will need registering.
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