There is no easy way to accomplish this.
For sso because 5.5 SSO does not have a database and the configuration can only be restored/backup for same versions . Same wo
Installing fresh SSO and Inventory service would not have that much impact on vCenter Functionality as vCenter Would still point to its existing database however in this case you would have to uninstall reinstall vCenter.
Also note that you before doing a fresh install of Inventory service check if you are using Storage Profiles in vCenter or any component which leverages Storage Profiles.