Hi @stuartrogerson good to see you active on the community again, I notice no one has responded so I will give my thoughts. bear in mind I don’t have a DTR2000.
Currently I believe you could use the DTR2000 as a replacement box. As you have BT as your ISP it should load a BT skin on your Retail box model.
You could also use the DTR2000 as a second (non subscription) box whilst still using your BT Tv box for your (BT subscription channels). Again as you are using BT as your ISP I would expect a BT skin to appear. The software rollout for the DTR2000 is a different path to the Bt boxes so there could be a few differences in operation and presentation at times ( although the skin is generally due to ISP you use) and range of apps may differ (eg Prime Video).
Your recordings and schedules and any paired mobile devices will be specific to each box.
If using both boxes in same room be aware that both boxes would pick up and react to remote control presses.