You would need to convince Plusnet to send an engineer to do a port swap, switching you from the ECI cabinet to the Huawei. OpenReach refer to this as a "lift & shift".
I don't know if it's even possible for them to do this. The system might just pick any free working port.
Convincing Plusnet to do this would be very difficult. Finding someone who understands your request might be a stretch.
Then they would need to convince OpenReach to change your perfectly working port.
It would likely set a precedent. Having both cabinet Vendors on the same PCP is becoming more common.
I'm not sure OpenReach would allow this.
I did what you want to do, but I ceased my line and reactivated it to achieve this.
I didn't even try requesting it as I wouldn't expect them to do it.
You could also try ordering a 2nd line in the hope that gets commissioned on the Huawei cabinet.
I don't think it is banded as with the DS SNR Margin at 3.4dB there isn't any more speed to be had.
The line is interleaved but the attainable isn't as high as I would expect.
Looks to me like the line has synced at 6dB, and dropped to 3.4dB some time after sync. This had lowered the attainable too.
I'd still guess the line is banded. It may even sync lower than that figure next resync though.