I realy like the game and i'm willing to help testing the PTS build. But when i wanted to join a message within the Insider Hub says after the join you need to reboot your xbox so i recognizes a new update and installs the PST version. Based on this it looks like it will replace the Preview version?

Could someone confirm this?

I'm willing to test but not if i have to give up my preview build version where i'm daily enjoying the game.

I am playing the Microsoft version and it replaced my Preview build.  Wait until they fix the issues if you are going to do the PTS.  I didn't realize this until I saw Grounded getting downloaded again on my PC.  

Wish they had 2 versions. A Preview and PTS in which one has the option to switch back and forth between without worrying about sharing the same save files.