It's all about the Software

Is there anything I need to specifically do when swapping from an sdrplay RSP1a to a RSPDX or will things 'just work'?

You just need to create a new Radio Definition.
SDR Console won't use your existing RSP1A definition because they are two different radios.
But other than that, no nothing else.

Thank you. As expected - it just worked after setting up a new definition