Ah, this is about a JVM running on a client machine, not a server. And the purpose is to prevent a user/client from running Java programs that have NOT been signed by a company developer? In that case, I think you will need to set up the client JVM accordingly (and then make sure that only an admin would be able to change it - and a regular user would hopefully not have admin rights).
"importing" is something you do in code. I assume you have done that in the 2nd app, because otherwise you could not write an app that handles objects of this class.
A ClassNotFoundException, on the other hand, happens at runtime when an app has been compiled with some class used in the code (SchoolData.Teacher in this case), but that class is missing at runtime. You need to add all classes an app uses to the classpath used when it is run.
This app can extract objects as files and writes on the harddisk.
So the 1st app serializes data in some fashion to files, and the 2nd app deserializes that? Which mechanism are you using for that?
Hybrid apps have long been past their peak time, since there are better approaches to achieving cross-platform compatibility - solutions like Flutter come to mind.
If you release the app under the same ID then it will be considered the same app. What impact that might have on ratings and downloads obviously depends on the overall quality of the app, which -if done well- is independent of its architecture.
Computers (definitely those running macOS and Windows) have built-in text search capabilities, but I take it that you investigated those, and found them lacking?
For purposes like these I use an information organizer - a piece of software where you can collect all those snippets of text, images, web shortcuts etc. that don't seem to fit anywhere else. For the Mac I like Yojimbo; I'm sure you can find some for Windows if you look online.