Currently the Coverity Connect instances defined globally in Jenkins hold the CIM connection information and credentials. However, this means that any job in Jenkins can use the global credentials to connect and upload data to any Coverity instance configured in Jenkins. This doesn't work well in large, shared, enterprise Jenkins instances.
If the Coverity plugin allowed the jobs to override the username/password supplied in a global Coverity Connect instance, then global Coverity Connect instances could optionally be configured without supplying credentials, forcing the jobs to supply them. This would prevent global access to Coverity instances, allowing the Jenkins job/folder permissions to effectively partition the Jenkins instance with respect to coverity. The Artifactory plugin, among others, does this.
Also this small enhancement could potentially have neat implications combined with macro expansion, such as using parameters or environment from the job to set the credentials to different users, if you wanted to stray from using a single account for Jenkins automation.