As I understand from your requirements here, you are seeking for 1 peoplesoft portal application that is integrated to other peoplesoft content providers, lets say HRMS and Finance and user should be able to change the password from Portal itself.
In this case, You could configure Portal 9.1 and integrate it with your applicaitons lets say - HRMS and FSCM through Single Signon (or Unified Navigation). After setting up SSO, you could create content reference link to these applications under Portal for Change Password Component. So whenever user click on these link under Portal, he will be navigated to change password page for the application (without asking for login credentials bcz of SSO). This way user can change the password in one application. After SSO, You could create cref with "CHANGE PASSWORD" component and use Remote Local Node of content Provider. This will open Change Password Page of Remote application ie. content provider (eg: HRMS) under Portal Header only. Once you have cref link of all application created, You can create a navigation collection (containing link of all applications) and publish that navigation as a Pagelet on Portal 9.1 Homepage
Understanding PeopleSoft-Only Single Signon, Press Enter to collapse
Now as you have changed the password, you want to sync the user profile and changes across all associated applications, this could be achieved by setting up "User Profile Syncronization" to sync same changes across all applicaitons.
Understanding User Profile Synchronization
Hope my understanding to your requirement is correct and above solution might be helpful. Let me know if it does, or otherwise I misunderstood your requirements.