+1 for a workaround. I'm a Jenkins neophyte, but would love a solution (e.g., using a groovy script and credentials plugin) as this is the one issue preventing me from automating my jenkins deployment.
I'm running into a scenario that I believe fairly closely aligns with this bug. I need to be able to change the user account that a pipelines credentials are associated with. I do not want to change the value on the pipeline itself because I'm looking at needing to be able to update the credentials for possibly hundreds of pipelines at a time and don't want to have to manually do that (sadly, due to operational requirements, automating pipeline creation using something like Job DSL isn't really an option).