Resolution:
(1)
PlatformXMLUpgrader is specifically used to update TIBCO BusinessStudio.
It checks if there are any new features added in the
installation setup under TIBCO_HOME\components (plug-ins/features) folder setup.
It also updates platform.xml which is under the BusinessStudio HOME directory.
This file is used by BusinessStudio during the startup to load the plug-ins in design time.

(2)
The Flattener tool is used to update the tra file passed on the newly
installed plug-ins; it checks for any new plug-in installations, their versions, dependencies and updates the tra file.
This is normally run against the template tra files (
createadminserver.tra ), and against the administrator server tra file in a cluster after any hotfix installations.