Dear Ravish,
You can publish API from portal or from gateway , but the application is only stored on portal side. I don't think you can add/edit application via /restman.
If you have portal 4.2, it has PAPI to manage application, please refer to,
Portal API (PAPI) - CA API Developer Portal - 4.2 - CA Technologies Documentation
You can find the CRUD of Application under section "Swagger File".
Regards,
Mark