Ok, I tried setting up the "buildnumber-maven-plugin", using Perforce. However, I couldn't get it to pull the P4 Changelist number correctly, and later reuse it within the "
upload-artifact-to-nexus" plugin.
To use a "custom artifact version number" in Nexus, I would need to create a "Staging Repo", push the Artifact as a Release with the custom code commit number / P4 Changelist number; then after end-to-end tests are done, use the "artifact-promotion" plugin to push the Artifacts to the "proper" Release project.
Basically, Jenkins has better support for Artifactory vs. Nexus. I'll be updating the pipeline to use Artifactory. If anyone has a better idea, I'd really like to hear it.