I found this in the documentation files:
https://wiki.unraid.net/Manual/Changing_The_Flash_Device
It says that the trial license will not work or even copied to the new replacement USB stick, but will remain forever on the old stick (although expire)
Now , booting the fully configured Unraid server (during the trial period) from the new USB stick will not start the array, until I have bought a license ...
So it seems to me, that the backup-configuration of the flash drive from the trial back-up (zip file) will work and start up the disk array with the new purchased license and the disks will not been reset to a blank status ...
Is this correct ?