Github user andrewmlim commented on the issue:
https://github.com/apache/nifi/pull/2922
Those trailing asterisks refer to the following sections.
From the System Properties section (line 2860-2861):
Consider configuring items below marked with an asterisk (*) in such a way
that upgrading will be easier.
From the Warning at the end of the Guide (line 3687):
Take care when configuring the properties above that are marked with an
asterisk (*).---
