Hi
First of all, you replied to this thread about three or four times which meant I had to go through and delete the posts then reinstate the latest one. Please be patient if you want to change something and your post hasn’t been approved yet.
Back to the topic, write to your strata manager and tell them you have had advice that their view is erroneous but you are taking their suggestion that you fix it yourself as permission to get the work done, after which you will send them a bill for the work done. If they have a problem with that, they can either raise it now or later at a tribunal.
And no, the cabling inside your lot is not common property so you need to fix that yourself. Nice try, though.