The standalone.last.xml generated for backup/history purposes differs from the standalone.initial.xml version beyond the changes done by the user.
I added a system property named foo but the diff between these two files shows much more diff's beyond what I would expect, some notable diff's are.

< <console-handler name="CONSOLE">
—
> <console-handler name="CONSOLE" autoflush="true">

< <periodic-rotating-file-handler name="FILE">
—
> <periodic-rotating-file-handler name="FILE" autoflush="true">

< <datasource jndi-name="java:jboss/datasources/ExampleDS" enabled="true" use-java-context="true"
< pool-name="H2DS">
> <datasource jndi-name="java:jboss/datasources/ExampleDS" pool-name="H2DS">

< <deployment-scanner scan-interval="5000" relative-to="jboss.server.base.dir" path="deployments"/>
—
> <deployment-scanner name="default" path="deployments" scan-enabled="true" scan-interval="5000" relative-to="jboss.server.base.dir" deployment-timeout="60"/>

< <mail-session jndi-name="java:jboss/mail/Default">
—
> <mail-session jndi-name="java:jboss/mail/Default" debug="false">