Let's use this silly example:

 resources:
   resA:
    type: foo
    properties:
      x: 1
      y: 2
   resB:
    type: foo

For the example x is updateReplace and y is updatable.

1. I change property x from "1" to "4" and stack-update, result: only resource A is deleted then re-created
2. I change property y from "2" to "3" and stack-update, result: only resource B is updated

Note: these field settings come from the underlying services that don't allow certain fields to be updated and are only available on create.