You can do this. The following are outside of the Part P Building Regs requirement:
he following types of work are non-notifiable:
Replacing accessories such as socket-outlets, control switches and ceiling roses
Replacing the cable for a single circuit only, where damaged, for example, by fire, rodent or impact(a)
Re-fixing or replacing the enclosures of existing installation components(b)
Providing mechanical protection to existing fixed installations(c)
Work that is not in a kitchen or special location and does not involve a special installation(d) and consists of:
Adding lighting points (light fittings and switches) to an existing circuit(e)
Adding socket-outlets and fused spurs to an existing ring or radial circuit(e)
Installing or upgrading main or supplementary equipotential bonding(f)