There is no need to migrate since the AS project is very much up-to-date.
Anyway, using the option found in Refactoring in AS (as you suggested), I get a message there are no usages (i.e. nothing to migrate).
In the original project, there are 4 library projects where one depends on the other 3. What I have basically done, is to compile the project, and use the 4 aar-archives in my wrapper (as I usually do) and then write my own classes on the top using such aar-archives and then create a B4A-wrapper. You may be right that there are duplicates of classes among the 4 aar-archives so that is something I should probably verify.
However, it is still odd that using the android.jar in the standard SDK, I have no problems compiling in B4A but with the other android.jar, I will get the error posted in my first post.
Just wondering if B4A somehow reads my Android SDK environment path which points to the standard Android SDK location and if this can cause any problems but then again, I have not changed anything, apart from installing the new beta, and everything, until yesterday, was working just fine.
I am going to uninstall my AndroidSDKB4A folder and create a new one. Maybe it got "polluted" somehow.