Currently any migration involving a c++ class and Blueprints that derive from c++ classes is workaround on workaround.
What Unreal engine needs is feature that would allow to migrate assets along with c++ classes and their links.
Desired behavior looks like this:
I have blueprint assets that are derived from c++ classes.
When I want to migrate them to another project, then I also specify base classes to the migration selection.
After migration is complete and target project is opened, the blueprint classes have correct c++ classes set as parent classes, and nothing is broken.
Also a possibility of reparenting parentless blueprint class should be added. Since now there is no valid fix for that situation, just a tedious workarounds.