Can the APM V8.1.3. Server user names be changed from the defaults?
The "itmuser" is created during IPM installation and so it cannot be changed. This link has more info:https://www.ibm.com/support/knowledgecenter/en/SSHLNR_8.1.3/com.ibm.pm.doc/install/planning_requirements.htm
It is not possible to use customer-provided usernames in place of the DB users (itmuser, db2apm) created by the APM server install.
Hope this helps!