You’d have to link both CBL 1.4 and CBL 2.0 into your app, and I can think of some serious problems with doing that. On iOS/Mac you’ll definitely run into class name conflicts. The same may happen in Java or C# if we’ve used the same package name (I don’t know if we have.) There are also serious SQLite problems that can arise if two versions of SQLite are linked into the same binary.
Can you explain why you’d want to manually migrate?