After upgrading to Portal 5.3 the following pop up is generated when attempting to update an API if logged into the portal as a non admin user such as an organization publisher:
"Do you want to retain visibility of " for this API? Clicking Yes may change the API from Private to Restricted."
Clicking the 'yes' option when the pop up is presented does allow the API to be updated successfully and there does not appear to be any impact or loss of functionality.
CA API Developer Portal 5.3
This has been identified as bug within the portal 5.3 release for which a fix will be provided in the 5.3.2 version.
The pop up message will have no impact on functionality in any way as the managing organization will not be changed if you choose the 'yes' option when that pop up is presented. Users that experience this problem can just select the 'yes' option when that pop up is presented as a work around for the time being.