If you're a previous RehearsalMix customer, and you connect your Planning Center account to your MultiTracks.com account-you'll lose access to all your previous downloadable mixes. Before you proceed you'll get a warning that this will happen.
All your previous mixes on Planning Center, will automatically be upgraded to the new format mixes. You won't need to re-add any previous mixes, once you re-link your account. To know for sure if you're on the new RehearsalMix platform, go to the site settings page on Planning Center. If the transition worked correctly you'll see (streaming) listed by the integration.
If you'd like to download your previous content you can login to RehearsalMix.com and click the download link on the pop-up to download your previous mixes.