@simonmaxhill - What you are describing (dynamic/symbolic linking of objects) is not currently possible using out-of-the-box Miro functionality. However, it may be possible to use Miro’s web SDK (or REST API if the objects are not on the same board) to accomplish what you are looking for. You would want someone with a development background to review the Miro Developer Platform documentation.
Feature request via Wish List Idea
Someone has requested very similar functionality in the following Wish List Idea - you may want to add your comments/vote here:
https://community.miro.com/wish-list-32/copy-objects-by-reference-instance-1008
However, if you fee that idea doesn’t truly reflect what you are looking to accomplish, I’d recommend adding this as an Idea in the Wish List category by following the guidelines here: Wish List: Everything You Need to Know.
If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.
Lastly, don't forget to vote for your own Idea.