Web UI navigation Change

We have installed on premise GitLab Server (version 12.4.2). we have a requirement to customize the project UI (GitLab UI).

The requirement is as follows,
Once we select a project in GitLab UI, we need to modify the GitLab UI to show a custom popup screen (to select an artifact associated with the project . These artifacts are populating from a 3rd party application). Once user select an artifact from 3rd party application, we need to show it in upper section in the project page - let’s say in a label or text box.

We are thinking below approaches.

  1. modifying GitLab project UI related sources
  2. write a server hook function (for project selection - currently this event is not available. can we create custom events? ) and render the UI from the plugin code.

is the option 2, a doable approach. then how can we integrate the rendered UI in a popup?

appreciate feedback from the community.