Actually thinking about it some more...
You can open two instances of MC if you set the flag in Options > General > Advanced > Allow multiple instances to run at one time.
So what you could do, assuming that the AK100_II library points to files on the AK100_II and has the tag updates, is.
Open MC to the Main Library.
Set the flag mentioned above. (Note that this flag gets reset to the default of unchecked once Mc is closed, so opening a second copy of MC only works once.)
Open a second copy of MC. If the Main Library is the default you will get a warning that it will be opened in Read-Only mode since it is already opened.
Change to the AK100_II library in the second instance of MC.
Use Views, searches, whatever to find the files that were updated in the MK100_II library.
Produce the same Views, searches, whatever in the Main Library.
In the MK100_II library, select the list of files that need updating, and press Ctrl-C.
In the Main Library, select the same list of files that need updating, and press Ctrl-V.
Theoretically, the files in the Main Library should now be updated with the tag changes. Test with one, then a few, then do them all.
Disclaimer: I haven't checked if this works as expected. I accept no responsibility for lost or damaged data or files, or for completely messing up your library!