Some monkey decided that the declared interface "wasn't exactly what he needed" and changed it.
This has nothing to do with updating the implementation classes automatically when configured so.
The issue you mention can be avoided by :
1. forbidding changes to the interface in the tool
2. forbidding changes to the interface in the review process
To implement 1. you propose to have "locked" interfaces. Why not, but it has nothing to do with the original issue.
By the way 2 is a valid option too.
Changing an interface is a major architectural decision
Not always, for example if you are in preliminary design phase or have control of all the depencencies.
(no, UML is not used only in giant project with big money)
But even when it's a major change in the project, it can be a necessary change. Then it's nice to have support from the tool to make it easier.