Hi James,
What i can see is that we no longer get the error pop-up, although there are visual clues on the upload table.
For cardinality changes you will need to select this as an option, and what you expect to see in the product

Once you have done this, if you break any of the data validation rules, you will see an error number next to the import item on that table.

However, the log file does not show this as an error

What I haven't been able to test yet is how Datalink responds to this, and I have an open question to that team to find out what we should expect. I should have an answer to this later today.
Michael