I try to move one of my LR 6 catalogs to the newfangled LR CC. I get the following dialog:

[![LR dialog][1]][1]

Why can I migrate *only once*? I am planning to do a test migration and then later with a new CC library a proper migration.

And is there a way to re-do the migration later despite Adobe's warning?

  [1]: https://i.sstatic.net/KPWDJ.png