Currently, we're maintaining few virtual services and gets regular updates to them. So, instead of maintaining a separate updates tracker, Is there any provision in DevTest Portal/ Workstation to keep the track of changes and notes ?
Version : 10.3
No, there isn't really.
A virtual service has its own development life cycle, just like the consuming component whose testing it supports. A good practice is to put the devtest project under a version control system (just like the source code of the consuming component). That VCS is most likely what your company already uses like git or svn or tfs or ...
The workstation has no interface to a vcs system to initiate a pull/checkout or push/checkin, so I always add a bin directory to my DevTest project in which I put a batch file which starts up the vcs client to do that action. You can double-click a batch file from within the Workstation project tree and it will start to execute.
In addition to version control it is also a good practice to adopt a semantic versioning scheme in the naming standard of your VSMs and VSIs. In addition to helping you keep track of changes it also allows you to do some assessments at runtime whenever you need to do root cause analysis, it allows you to easily assess if the functionality deployed is the one you expected for some particular test run.