Is there a way to rerender a symbol on a bubble layer when the data item for it is changed?  I can probably make it work by copying the whole data source, emptying it, and then copying it back in with the updated values, but that seems like overkill.  I just want to be able to change things on some symbols.

Hello,

One approach would be to change individual model items. The layer will be repainted accordingly:
  BLOCKS.data()[0].set("Location", [0, 0]);

Alternatively, you can keep a reference to the rendered visual. It remains live and will respond to changes, e.g.
  symbol.children[1].text("Foo");

I hope this helps.

Regards,
T. Tsonev
Telerik