I have covered this before but only as part of other peoples threads (with many thanks to @wheelbarrow01).  Given that I am trying to do this a second time and experiencing difficulties when I had no difficulties the first time I thought it worth a thread of its own.

With Chorus ONTs there are multiple ports (4 on the model 300).  In normal times only one is used.

It seems clear to me that most users are transferred from old to new RSP.  This leaves them vulnerable to an outage (no service between disconnect from the old RSP and connect to the new one) which may be just a few minutes or maybe a few hours.  If there are problems with getting the new connection up then the user if live-testing a faltering new connection.  For those with a homeline to be transferred this is the only option - but for naked users there is a logical alternative

Whenever I change my RSP I prefer to use an pay for an overlap period - ie the new RSP connects before the old RSP disconnects.  This gives me the opportunity to test the new RSP prior to losing the service from the old one.  This is only possible with naked Fibre, because there are multiple ports available on the ONT.  When I moved from Orcon (port 1) to Voyager (port 2) just over a year ago I did exactly this and it worked.  I had the Orcon router plugged into port 1 and the Voyager router plugged into port 2.  The overlap period was 5 days.  I was able to unpack the Voyager router and get it set up an working while the rest of the household continued to use Orcon.  After the Voyager router had been up for a day or 2 I cut the rest of the household (about 10 devices) over to the Voyager router.

Now I am moving from Voyager to Sky broadband.  The key determinant of dates is Voyager requiring 30 days disconnection notice so Voyager set a disconnect date of May 28th.  However Sky have been unable to schedule a connect on May 20th (my choice) on port 1 (unused) because they say Chorus will not accept it - because of the Voyager disconnect request must be actioned first before a subsequent new connection request can be made.  Voyager will only say that they have issued a standard disconnect notice to Chorus (ie I dont know whether they specified port 2 or not).  I can only go so far as an end-user because there is no way I can contact Chorus direct.

I have lodged a complaint with the Telecommunications Dispute Resolution (TDR) organisation but this is not their brief (Chorus is not a member) however they have forwarded my complaint to Chorus so maybe something will come of this.