You are right. I thought about that too .. The problem is :
"The change-master-password subcommand is used to modify the master
password. The change-master-password subcommand is interactive in that
the user is prompted for the old master password, as well as the new
master password. This subcommand will not work unless the server is
stopped. In a distributed environment, this command must run on each
machine in the domain."
So I don't expect to work with a postbootcommandfile either. I tried it and I receive the same warnning :"Feb 09, 2018 11:02:03 AM fish.payara.micro.boot.runtime.BootCommand
WARNING: Boot Command change-master-password failed Exception while executing command."
I also tried to specify a ROOT_DIR and there in the config folder to create a master-password file with the new password, but it didn't work.
I am running out of ideas.