Can we set beta channel of public app in policy?

We have an application published on the play store that is used as require for setup app, I have different channels in play console, production and beta/closed. 

In AMAPI policy, we can set "accessibleTrackIds": [ string ] so that a particular channel is used to download the application.

Here is the issue, when we go to the advanced settings in the play console for the app and turn on Managed Google Play, it shows that the app will become private and this can not be undone.

Is this the way or we can use the public application's testing channel by specifying its track id in the policy and it will download for eg. if beta is added then it will download the beta channel app and if there is no track id mentioned then it will default to the production application? 

Another thing is that, how to get the track id in case we can do this?