The Medway Handyman wrote:

Which ones would you suggest require testing?

- Replace light switches . . . . . . . = repair/maintenance
- Fit dimmer switches . . . . . . . . = alteration
- Replace ceiling roses . . . . . . . = repair/maintenance
- Fit Ceiling Fans . . . . . . . . . . = addition
- Replace damaged sockets . . . . . . = repair/maintenance
- Convert single sockets to two way . = alteration
- Convert double sockets to three way = alteration
- Convert single sockets to four way . = alteration
- Any 'like for like' replacement . . = repair/maintenance

The additions and alts certainly do; for the repairs and maintenance
items it's a moot point, but do read 1.13 in the Approved Doc.

- Fit outside lights = addition, and notifiable in some circumstances.

(provided that cable terminates in a 13amp plug)

It's another moot point whether that gets you off the hook. You are
still adding fixed electrical equipment and presumably fixed wiring
thereto, forming part of a fixed electrical installation and therefore
within the scope...

I asked my local Trading Standards [...] but of course they aren't
electricians.

Quite. Sadly, it's probably your PL insurance company that will have
the final word. If you are going to certify they will probably insist
that you get the C&G 2381 & 2391 tickets (not that those are
particularly difficult if you know your stuff). That would then give
you the advantage of being able to do notifiable work for just the cost
of a building notice and minimal fuss (see 1.22 in the Approved Doc.)

--
Andy